Windows 7 RC1 will be released on MSDN on april 30th. There is a very nice review/ preview on the windows supersite. From my experience so far (from the public beta):  it’s very slick and snappy. The ui is a lot better too, especially the task bar. It stacks the programs in a much nicer way, and you can easily switch between windows etc.. But read the extensive review below for (much) more info .

But Windows 7, in release candidate guise, is already a towering achievement that casts Windows Vista immediately in its shadow.

Microsoft’s Windows 7 Site

Windows 7 RC1 Review