Sure you can :-D
If the Optimus isn't every geek's wet dream, I don't know what is.

I just use my trusty IBM Model M as my gaming keyboard, and will be VERY hard-pressed to replace it, for I still have yet to find a keyboard that can even compare in terms of key feel. (About the closest I've found is an Apple Extended Keyboard II, but the ones I've tried have a mushy feel to their keys now. At least the keys themselves have good travel. I haven't tried a Cherry board or Das Keyboard yet. I have tried a Logitech G11 at a store, and the keys feel like your typical cheap rubber dome crap.)
As for the mouse, I got a Logitech G5 2005 a few years back as a Christmas gift. It could use an extra mouse button, but it's a good mouse overall. (However, the best mouse would probably be the MX1000 made wired and retrofitted with the G9's laser sensor. Can't beat having all of those buttons.)
For gamepad-oriented games, I use both an Xbox 360 wireless pad (fior XInput games) and an original Xbox pad with the XBCD drivers and a spliced normal USB cable (for DirectInput games).
For the flight sims, I have a Thrustmaster HOTAS Cougar with a pressure-driven stick mod installed, and a set of Thrustmaster RCS pedals with a Hall sensor kit installed connected to it for rudder (the stick doesn't twist, and the throttle has no rocker, as F-16 HOTAS design specifies). It was expensive, but worth every cent.
Finally, I have a NaturalPoint TrackIR 4 Pro. It's mostly used in flight sims because it lacks support outside vehicle simulations, but it's also rather valuable in Armed Assault even when on foot. It does wonders for one's situational awareness, and frees up that hat switch on your joystick for better things.

Personally, I'm fine with simple. My keyboard is an old PS/2 one I inherited from my place of work about three jobs back. I'm guessing it's about 10 years old. No fancy media buttons, no weird ergonomic design, nothing. Just a plain old slightly rough-finished beige-going-on-brown (I really should clean it one of these days) perfectly ordinary keyboard. But I'm used to it. It's served me well, and I don't think I'll part with it until it breaks down.
My mouse is an old wired optical Microsoft 2-button scrollwheel mouse. I prefer a wired mouse over a wireless one for gaming. I think wireless mice are too heavy for that. I'm afraid it would slip from my hand and I'd accidentally throw it across the room when playing UT2004.
I'm thinking of getting a new mouse for ordinary Windows usage, though. I just got a Logitech MX 620 Cordless Laser Mouse at work, and I gotta say, I absolutely love this thing. The gearless scrollwheel is so great, and just the thing for scrolling extremely fast through, for example a long code file, or for that matter, the GOG forum. So I'll probably get one for my home PC one of these days, but I'll still be using the old wired one for gaming.
I also own, but don't use, a couple of somewhat more esoteric control devices. Sadly, both of them are old, and do not work on modern versions of Windows, so I keep them mostly out of historical interest.
Logitech WingMan Force Feedback Mouse
This is brilliant, in a cool-and-interesting-but-not-terribly-useful way. It's not like the modern "vibrator mice" that pass for force feedback devices nowadays, or did a few years ago anyway, it's been a while since I've seen any of them. No, this is a proper force feedback device, meaning that if you play a game and run into a wall, for instance, the mouse will actually jerk backwards in your hand. The downside is that it's mounted onto the mousepad it comes with, and cannot be lifted. This puts a damper on normal mouse operation, and so it doesn't really work like a mouse, but more like a track plate or something. What this means is that if you're controlling a pointer (on your Windows desktop for instance), each corner of the mouse pad maps directly to each corner of the screen.
Here's the other one:
ThrustMaster Pinball Wizzard Controller
How cool is this? Well, unfortunately I have no idea, because I've never gotten the damn thing to work. Still, you can't deny the retro-geek factor :-D

I remember seeing that force feedback mouse and thinking it might be a good idea but then never found one to buy.
So for a mere au$2500, I could get one of the swankiest keyboards ever made? Yeah that or I could spend it on further improving the new gaming rig I'm planning and get a Core i7 and GF GTX295... The only things I've got to plug the keyboard into is my laptop and my old 1ghz athlon internet machine which probably has less processing power in total...

I've just gotten my Krait, and it is awesome. Sure, it doesn't give me extra buttons (so I can't do on-the-fly sensitivity changes without sacrificing scroll button clicking), but it's amazing. The orange glow kicks ass, and the Teflon feet makes gliding to smooth. Well worth the money.

I covet those separate keypads with configurable and programmable keys you can move all over. Partly for the power, even a little bit for the geek thrill of it, but also because keypads on keyboards are to the right, and if you want to have a keyboard centered, you're either twisitng to the right for hours or moving your keyboard way over to the left, which takes up a lot of room and if you're on a laptop is not really workable.
I got Decent here on GoG and I remember loving playing it with a joystick and keypad combo. I'm on a laptop now and putting and so making adjustments by moving stuff or me around is a no-go. But a joystick I could put on my right and a keypad I could put on my left would be great. Looking at one of the CH flightsticks for the joystick part. My friend had one of those and it didn't feel quite smooth, but they are very durable and overall well made. I've had Saiteks but they tended to have dead spots and/or jump around a lot even when the stick was still, and I loved my old Thrustmaster HOTAS combo from years ago but the new ones get horrible reviews. So I'll be on to CH products even though they're not my first or even second choice.

Not really sure what makes a "gaming" keyboard or mouse, but for me it was a matter of comfort and functionality when choosing my keyboard and mouse (Saitek Eclipse and this mouse). I'd say comfort is the top factor between the two, though, as ending a 4 hour gaming session with sore fingers and wrists isn't too fun. In this respect I'm quite happy, as both my keyboard and mouse are very comfortable to use, especially when coupled with a padded wrist rest on the mousepad. Some additional functionality can also be nice, though, as a few of the extra buttons on the mouse were nice to have when playing Descent 3 (doesn't do much for non-twitch games, though, so I don't end up using them much).

for me gaming periphecials must be "user friendly" and nice :)
Long time i was living with stock mouse and keyboard, then i got wireless set for xmas, used it for two days (in ravens words "never more")
now i am using
Logitech G15 (old one) http://upload.wikimedia.org/wikipedia/commons/0/0d/G15.jpg
its like M2 HMG - heavy and hard hitting, i never used panel, macros, or any of those gadgets included, i just like its weight and hard buttons.
Razer diamondback plasma http://www.vmart.pk/main/images/razer%20diamondback.jpg
it is fairly light, and i have razer mantis control mousepad, so it is just so great :) but i dont use sidebuttons, only main left, right and sometimes scrolling wheel.
And if i am desperate enought i put out my old belkin nostomo N52 speedpad http://www.belkin.com/images/product/F8GFPC100/PRN1_F8GFPC100.jpg
it is real gaming gadget, i am too lazy to instal drivers, but when i have them, this toy is alltime in my hand.
maybe this year i will try OCZ NIA http://www.ocztechnology.com/products/ocz_peripherals/nia-neural_impulse_actuator