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Based on Microsoft's past OS releases, early adopters will be advanced beta testers.
My advice would be to save the money and buy a new computer in a year or so, with W7 installed, after it's been patched up with a couple new service releases.

The only reasons I can see for someone not to upgrade to Win 7 is if they can't afford it, aren't comfortable doing complete reformats and reinstalls, don't need it, or simply don't want it.
But fear of being an "advanced beta tester" or the OS being broken or something are not in the mix, IMO. I've been using Win 7 since April or May, on two different PCs with entirely different hardware configurations and have had no problems with it.
For home users, that is. I do think it's good advice for businesses to not jump on the latest OS release unless they've been testing it out and know it will work for them.
And of course it also has a lot to do with your own overall experience. I might lose half a day at the most if an OS dies or causes problems and I have to reinstall everything. For other people that could be a week-long exasperating affair, requiring outside help.

I also have a PC running XP on it, but that's just for my very old printer and scanner, which I need XP for, since I can't get any drivers that work for Win 7 (or Vista). I hate even turning that machine on, because it's so sluggish. It only has a dual core AMD @ 3.0 ghz and 4 GB of RAM though, so it's a pretty weak machine to begin with.

Windows 7 is a ginormous improvement over XP and a huge improvement over Vista, as well, in many, many ways.