I have setup my Exchange 2003 SP2 server to get rid of quite a few annoyances that give end-users fits. One Microsoft fix has given me some undesirable side effects. I used this method to bypass the need for the end user to enter their domain\username at the OWA logon http://support.microsoft.com/kb/903942
It works like a charm except for the two following items, at least these are the only two items I have noticed to date.
If you logon to OWA without entering the domain:
1) Links require you to reenter your username in the form of domain\username and the password to open up links. The password box pops open when you try and click on links.
2) Spell check fails when you reply to an email in OWA. For some reason spell check works fine in newly constructed email in OWA but fails in a reply.
I haven't been able to find out any documentation on how to fix these items or if it is even possible. They aren't critical but they are definitley annoying.