I rolled out Exchange 2003 SP2 this past weekend, a few days after it was released.

Noticed several administrative annoyances/comments/notes:

• Public access locations (IIS Virtual Directories, POP3 server, SMTP server, etc...) have their permissions reset.  If you've disabled Integrated authentication due to compatibility problems (I use Basic with SSL encryption) all your clients won't be able to login.
• Side note: best solution is to add alias to FQDN and make them login with their full email address instead of using AD username!
• Calendaring control suddenly stopped working.
• Flushed out MIME types - http://www.exchangeserverhelp.com/ftopic1959.html had a similar problem with them.  Strange thing is, it didn't break anything until AFTER SP2 was installed!
• Backups
• Make sure you reselect the folders for backup in Veritas.  Double check your backups work!
• F-Secure for Exchange 6.40 works fine with 2003 with SP2.  Lovely. =)
• Wait for the mobile upgrade pack to enable more functionality with push email alerting!