Ars Technica posted a roundup of all the UI changes between Windows 7 build 7000 and Windows 7 build 7100.

Earlier this month, Microsoft made the Windows 7 Release Candidate build publically available. The flood of e-mails began: "Emil, what's new in the RC? What changed? What is different?" That question can be answered in many ways. Some of my peers have already reviewed the RC build, and while I commend them on their effort, reviewing beta software is not something I personally like to do. If you want the short answer to the question, I will tell you this: there are thousands of bugs fixed, the build is much faster all around, and most importantly, the biggest feature changes have been completed. If you want the long answer, and I mean the really long answer, read on.

First thing is first though, let's have a look at the compilation times to see how much work we are trying to track. There is more than four months difference between the two builds: the beta (build 7000) was compiled on December 12, 2008, at 2:00pm and the RC (build 7100) was compiled on April 21, 2009, at 5:00pm. As you can see in the screenshot above, build 7000 officially expires on July 1, 2009, while build 7100 expires on March 1, 2010. After that date, the RC will begin to shut down every two hours. Of course, the RTM build of Windows 7 will be available long before then. For now though, if you're still on the beta, I would recommend moving over to the RC (via a clean install if possible) as soon as possible.

Side by side: UI changes from Windows 7 beta to Windows 7 RC