For those of you waiting with baited breath, and possessing a spare machine that you can afford to render non-functional or have a Virtual PC license, get IE 7 beta 3 now.
From what I can tell it does not have any significant rendering engine changes from the preceding beta. It does contain some security updates, so users are strongly advised to update. Biggest visible changes are draggable tags (a la Firefox 1.5) and the ability to mark RSS feeds and posts as read. You can check out documented changes in the release notes.
Also available is the IE7 Readiness Toolkit which contains a fair amount of handy information and links to tools that will help prepare us developers for the onset of IE 7 later this year.
I would also advise checking out the IEBlog on a regular basis. Related to this release, I would definitely take a look at the very good summary of the UI changes and a handy how-to uninstall preceding betas guide.
[NB: Announcement just hit all wires, IE blog appears to have gone offline while I was writing this. IE7 downloads will probably be a bit slow tonight.]