The first Windows 7 beta reviews have been pretty positive; possibly too positive. Now Ars Technica published an in-depth review of Windows 7 and their verdict at the end has some statements in there that point me back to my hard decision on switching to Mac after all these years.
Quote from the review: "Let's just cut to the chase here: Windows 7 is built on top of Windows Vista. It doesn't roll back the major changes that Vista made; it doesn't reduce system requirements (for example, it still needs Direct3D graphics and 1 GB RAM to be worthwhile), it doesn't undo security decisions like UAC, and, except for specific scenarios like booting, it doesn't really perform significantly better. However, Windows 7 shouldn't make anything any worse."
Read the full in-depth Windows 7 review on Arstechnica.

One other major problem is currently the IE8. Apparently it is so unstable that it is not usable. There is still a lot of work for Microsoft to get Windows 7 out the door and it is still uncertain if this will happen already this summer.

Microsoft removed the 2.5m Windows 7 beta key restriction and you can still download Windows 7 beta 1 for yourself until January 24th.
In case you need instructions on how to install and test Windows 7 beta, Gizmodo published an easy guide.