...the thing is, it says it has DRM... but its an interesting product, and includes Civ IV: Colonization. Has anyone experienced that gamersgate version and know exactly what kind of DRM are we talking about? Is it 'harmless' or is it draconian-you-won't-install-more-than-5-times type of thing?...

Go out and buy the boxed version; I believe that it is DRM free. At least I own the boxed version and do not think it has DRM connected to it.
Here are a few links for you.
GoGamer
Buy.com
Amazon

If you're concerned about the DRM you can either email Gamersgate support and ask them, or try asking them via Twitter. They tend to answer fairly quickly.
But if it does have DRM, it'll most likely be online activation via SecuROM -- with no activation limits/infinite revocations.

Bansama is absolutely correct, zM. I have the GG version, and that's what it uses.
And actually...once you use the in-game patchers to update, you might not even need to DRM anymore. You might be able to uninstall the SecuROM and not have it come back. Not 100% sure because I haven't had a chance to do it yet.

Can you buy from Play.com? Only they're offering it for £5.

Play.com version dosen't have Colonization expansion, but for that price (6.49€) its amazing deal (one that I ordered too).
Play.com offer dosen't include Colonization expansion, but for the price of 6.49€ posted to Europe it's great deal. I purached that too.