According to a TAP group member, there are major bugs that have been found in build 5259 of Windows Vista by TAP testers.
As a result, Microsoft is working on compiling a new build. At this stage, Build 5262 is likely to be released on either Monday or Tuesday. It is also possible that Microsoft will release build 5259 "as is" on Monday or Tuesday, but advise people with specific configurations to be aware of the major issues.