OCC has published an extensive review of the Windows 7 Beta. Here's a taster:

Right now, Windows 7 may not be the fastest operating system, but it feels better than Vista ever did and is extremely fun to use. Boot up times seem to have increased, while logging in and waking up from sleep or standby is definitely quicker. The refreshed Aero interface for transparent windows is a small but pleasant visual upgrade, and the automatic maximizing of windows when you drag them up top is a new and interesting feature. While I did experience a few bugs, the occasional crash and a few obnoxious features, they can almost all be chocked up to the fact that this is still an unfinished project. There is still room for improvement, and I'm optimistic Microsoft will make sure Windows 7 is the XP killer. With the vast majority of netbooks running XP, Redmond's software giant really needs something to make manufacturers move on to something newer. After having used Windows 7 as the main OS for a few weeks now, I can say it runs surprisingly well. The underpowered Atom coupled with a slow hard drive and 2GB of RAM was enough to tame 7.

In the very unlikely event that Microsoft makes no changes at all, I would still choose this OS over Vista any day of the week. Sure it does use a lot of RAM, but with memory prices as low as they are, you'd be better off to get a couple more gigabytes than stick with eight year old XP. Let's face it, XP has lived a long and successful life. Somebody buy it an aluminum walker! One of the main reasons it has lived for so long is that it runs on barely half-decent hardware. However, with hardware quickly progressing and getting faster every day, handling a relatively "heavy" OS is not much of an issue anymore. Honestly, Vista was ahead of the mainstream hardware and that explains the bad press it got and still receives. Windows 7 may not have all that much to offer you over XP or Vista, but you will have to upgrade eventually and the way I see it, the sooner the better. Even though there isn't anything clearly revolutionary, it adds a bunch of small things that make the whole experience that much more interesting.

Pros:
- More transparent windows
- "Stretchy Windows"
- "Sexy" maximization
- Miniature windows
- More user friendly taskbar
- Improved right-click on desktop
- Easier personalization
- Easier access to UAC control
- Fast login times

Cons:
- Random crashes
- Clicking icons brings up already open ones
- Tabs slow to open in IE
- Slow boot screen
- "Show Desktop" button moved to the bottom-right corner