I downloaded a copy of Windows 7 (beta build 7000) over the weekend. It loaded onto my t40 in about 30 minutes with 2 reboots. This was pretty good - not as fast as Ubuntu Linux, but faster than XP.
Over the weekend I found that it boots quickly, and shuts down well. It comes up from hibernate with no trouble. It had no trouble with any of my HW. Wifi worked well, but seemed to work better when I explicitly told it to connect to a network when comming out of hybernate.
Esthetically it looks very nice. The text is clean. The colors bright - no more grey or blue everywhere. Everything is very minimilist - no extra pixels wasted on useless information. This is great news as the job of an OS is to melt into the background so you can use you APPs in the foreground.
I like the new Taskbar. It works like OSX's dock in that your apps have a little icon on it. However, unlike the dock, it doesn't have an icon per open window. Instead open windows become available when you hover over click on the icon. I like this since your running apps don't move around making them easier to find. That is, in OSX, when I minimize a window, it goes to a different place than I launched it from.
The new Start Menu us trimmed down significantly from XP. For one it isn't name Start - in itself a HUGE improvement. Microsoft used good color schemes to deliniate between your programs and those items that interact with the system.
The Control Panel is very much improved over XP and even more so over Vista. As in elsewhere in the OS a minimalist aproach is used. There are "advanced" options, but the most commonly used options are righ there in front.
There was on dark spot. Can anyone explain to me why only Apple ships an OS that plays DVDs out of the box? Linux can't, I know, because the codec's are licensed. MS windows 7 can't either???? I was pretty disapointed when I put in a DVD and it said it couldn't play it. To paraphrase the error: I can't play this DVD since your output device (the monitor) can't be copy protected. Hey DVD content providers (and Microsoft): This is STUPID.
All in all, I liked windows 7. I'm going to keep it on this machine for a while... If you like, you can take a look without installing it.