I've been running Windows 7 RTM (the final version) on my Thinkpad X31 for almost a month. Got it off my university's MSDN-AA site. I haven't tried the betas or the RC before.
The specs are Pentium M Banias 1.4 GHz, 1 GB DDR DDR-333, ATI Mobility Radeon 7000 (16 MB VRAM), 80 GB Seagate 5400.3 ST980815A (peak throughout around 45 MB/s
), Intel PRO/Wireless 2100 3B. Laptop was built in May 2004.
It shipped with XP. Had Vista installed on a 40 GB 4200 rpm drive when I got it, and the less said about that phase, the better. I've ran XP as well as various versions of Ubuntu on it. Most recently, it was slumming it out with an install of Kubuntu which evidently went horribly wrong at some point, as every disk access was oh so slow.
I'm using it pretty lightly, almost a glorified netbook, primarily browsers (Chrome + Opera), putty, foxit, occasional remote desktop.
It works. No problems. Satisfied.
It feels a bit less instant than XP at its best, but I am happy to trade that for an OS that feels 2009. The changes from Vista don't seem to be major, but what I did notice, I liked or was at most ambivalent about. Can't say I ran into something I used in XP or Vista that doesn't work satisfactorily in Windows 7. Most Ubuntu installs I've had eventually got frustratingly slow on disk access for reasons unknown (2-3 seconds to bring up Alt-F2 box), and this is better so far. I've installed Microsoft Security Essentials package, more for the peace of mind than anything. I think it slowed things down a little bit, but it's definitely still acceptable.
For my use, 1 GB is fine; sometimes when I sail north of 15 browser tabs the system feels like it could use 2 GB which is the max on my system. Alternatively, a faster hard drive (pretty much anything you can buy these days) would also help, but I haven't bothered.
I'm not running Aero because of the ancient video card. The basic interface seems fine.
This wasn't supposed to be my primary computer, and I think that's the best way to try the OS. If you don't have a second computer, try to throw up a VM, and just see how you like it. This seems like a bad OS to fight and insist it do things your way or the way you're used to; sorry if this seems Applesque, but I do think letting it do things on its own is a good idea.