I've been running Windows 7 since the RC and am currently running the RTM version (from technet). I figure it'd be helpful for some people to see my experience with the OS before they make their decision.
For starters: I HIGHLY recommend this operating. It is everything Vista should have been, but it is much more than a Vista Service Pack.
If you have the ability to run the 64-bit version, I highly recommend going with that. I have had almost no issues (except for some random 3rd party programs that were poorly coded)
I'm gonna start with what I don't like...there isn't much. The thing I hate the most is the control panel. It is still a disorganized mess. Using classic mode, it still takes a while to find things...hopefully there will be improvements made to this. The second is off of this with the networking controls. The networking itself is much improved, but the interface is very roundabout and you can end up going around in loops between a bunch of screens to get to what you want. That's it...Those are the only 2 things I hate about Win 7.
Things I like: The Start Bar. This is a huge improvement in usability over XP. I love it, and use nearly all the features on it. The jumplists make access easy (though only a few programs support it off the bat (firefox does not, chrome does). I pin the programs I use most on there and rarely have to invoke the start menu itself (which is nice). If I need another program, just hit the windows key and start typing the program name.
ALT+TAB is dramatically improved, and helpful for switching tasks. If you want to take it a step further, WIN+TAB blows out all your windows for switching, which is pretty useful as well.
Libraries: I've been wanting this for a long time. If you store a lot of media or documents and the like and they are scattered across multiple drives and folders, this can make it a lot easier to track and organize the content for sharing or what not.
Performance: I used Vista for a week before I went back to XP because it was too slow. I have 8GB of RAM in my PC. XP wasn't using it. 7 Uses it all and runs just as fast as XP. Taking into account the user interface upgrades, my productivity has increased a lot (it took a bit of time to get there and get used to everything. I now find myself flipping through and trying to access those features on my XP PC at work...wishing they were there.
Stability: I run my PC hard...I do a lot of things on it, and I rarely restart (updates being the only reason). I had XP running pretty stable...but occasionally a driver would take down the system. It was a fact of life. A game or something would just hard lock a driver and there'd be nothing I could do about it. I don't remember an instance since May 2009 where I've crashed this PC while running 7. If a game hard locks on a driver, the computer will freeze for about 10 to 15 seconds while I can still move the mouse. You do some fiddling with alt-tab or try to invoke the Task Manager, and Windows will some how unlock itself and kill the offending program. Then continue running like nothing happened. Still pretty impressed with that.
Installation: Upgrades can take a very long time...I don't recommend it. Back up your applications, then download an installer from something like ninite.com (to install your common apps in one shot). The full fresh install of 7 took roughly 45 minutes on my desktop...with no real fiddling with drivers. I just needed to pick up updated drivers for a few things. By far the smoothest install I've had.
Again, I think this is one of the best OS's Microsoft has turned out so far, and I highly recommend it.