Make sure YOU HAVE PROPER BACKUPS BEFORE YOU INSTALL 3.0.
Grundle has been having some trouble and I don't want anyone else to get their phone hosed up.
(we got him all squared away, but still don't do it to yourself)
Sync your phone at minimum and if possible sync your contacts, email pictures etc somewhere outside of itunes. Outlook or whatever you use.
If you do bork your phone then use this sweet piece of kungfu on a mac to extract your old backups
http://ericasadun.com/ftp/Macintosh/mdhelper