AlKim: Let's face it, you are more likely to spill a drink on your keyboard than the monitor or motherboard.
True, but then modern laptops are nowadays usually designed with failsafe systems that some drink spilled on the keyboard does not go to motherboard, but goes past. Of course if it gets soaking wet... anyway, considering how long I've been using laptops and desktops, I don't recall ever spilling my drinks on them. I guess I am a careful kind of guy, taking backups and all.
Anyways, when I think about the cases when something on my PCs has gotten broken, the desktop has been just as unusable as a laptop would, until I got a replacement part. For example, my desktop PSU died so I couldn't use the computer until I got the replacement PSU. Or, I've had my USB ports getting broken both on my desktop and one of my laptops. In both the workaround was the same: for the desktop I bought an extra PCI card with extra USB ports, while for the laptop I bought an ExpressCard with extra USB ports. (ok, not all laptops have expansion bays...)
If my laptop keyboard got broken... I guess I'd use an external USB keyboard with it, until I got the replacement part (laptop keyboard).
AlKim: Using an external keyboard makes fairly little sense to me
If you are happy with the laptop keyboard and are using the laptop screen, I guess not. But if you are e.g. using an external monitor or the laptop is connected to HDTV, heck yes.
AlKim: Okay, this was fairly new to me. I've seen spare fans and such, but not screens.
Well, it isn't like the laptop keyboards or screens are soldered to the laptop motherboard or anything. :) For example when the screen on my Compaq work laptop broke a long time ago, the maintenance guy came in, took the replacement screen from the plastic, opened the system a bit, and replaced the screen. I think it took a few minutes for him, but I guess he had done it several times.
AlKim: Not that I've had reason to look for them, mind you. I've disassembled a few laptops over the years, though, and it was nightmarish every single time. No idea whether modern laptops have fewer and more obviously located screws and such, though.
Always a good idea to google for the HW maintenance manual for your specific laptop, but I'd say replacing the fan for a T400 is not that much harder than what I had to do to replace the PSU on my desktop.
timppu: Don't forget though that you can connect monitors and USB keyboards to laptops too.
AlKim: To me, this sounds unnecessarily expensive and rather retarded. I've seen some people plug screens and keyboards to their laptops and basically use the laptop as a slim desktop and I've never understood why they did that. I can sort of understand this kind of behaviour if you like the superior ergonomics of a desktop but need a laptop during lectures or something, but these people didn't. They might as well have bought a desktop to begin with.
At least at our work the employer hasn't bought us desktops for like a decade, even if you wanted one (I didn't, because I need the mobility also at my work, sometimes going to meetings and sometimes to the HW lab, oh and sometimes doing the work from home instead).
Depending what kind of laptop keyboard you have (chiclet? Ewww...) and how small the screen is, using an external keyboard and monitor can make a lot of sense if you need to read and type a lot. I do that too occasionally because the monitor at my work is much bigger than my T400 screen (=higher resolution, and easier on the eyes), and then there are those freaks with multiple monitor setups.
I don't see connecting an external keyboard or monitor to a laptop anymore retarded than connecting an USB mouse to one. Sure laptops have touchpads, but why should I be restricted into using only them if I don't want, and feel mice are superior pointing devices for serious use?
(Writing this from an ancient (2005) Dell Latitude D610 I borrowed from work today, in order to install Mint Linux 14 on it. Using its own screen and keyboard, but an external USB mouse. The D610 keyboard is great, feels just as good as the ThinkPad T-series keyboards I like so much.)