In case you somehow missed it, Service Pack 1 beta for Windows 7 and Windows 2008 R2 is now publically available.  Information on getting the download and support for the beta is located here:

http://support.microsoft.com/kb/976932

A couple of quick notes in the event that you dont read the entire KB:

1.  There is no official support for the beta, newsgroups only

2.  Please read the release notes prior to installing the beta, it can help you in avoiding a couple of the known issues we’ve seen to date

I’m sure I’ll end up speaking more to the Service Pack as we get closer to RC and RTM, but for now, all I can say is that I have been running it at work without much of an issue for a while now.  There are two new features that are enabled in the beta for Windows 2008 R2 installations, dynamic memory for Hyper-V virtual machines and RemoteFX for RDP clients (very cool btw).  More information on each of them can be found on the following blog entries":

Dyanmic Memory: http://blogs.technet.com/b/virtualization/archive/2010/03/18/dynamic-memory-coming-to-hyper-v.aspx

RemoteFX: http://blogs.technet.com/b/virtualization/archive/2010/03/18/explaining-microsoft-remotefx.aspx

--Joseph