The rules for U.S. daylight savings time are changing in 2007. SourceSafe cares about time zones, so you should too. Complete details are in KB article 931804. To quote one section heading, "If you do not update the servers and client computers, you may lose check-in information".
There, do I have your attention now? 🙂
[Thanks to everyone who helped put this article together. People inside & outside of MS often complain about the difficulty of maintaining the KB -- rightfully so in some cases. This article went from idea to the web in under a week, so it can be done!]