1. The Crossed Out Email Titles:

Alright, I get the purpose of it. You move an email into another folder, or you delete it - and instead of just disappearing, the email is crossed out and so you know that it has been moved. This is helpful if you want to undo the move/delete - or if 2 days later you are looking for that one email that you swear was in the inbox...
But I mean COME ON! I moved it into another folder for a reason! or I deleted this crap, so why is its ghost still haunting me.
Note: This may be because my email service is setup on an IMAP server, but it still doesn't make sense. Why Bill Gates - WHY!? He must be using Thunderbird or something ;)
2. Outlook won't import a Thunderbird address book!

So it exports Outlook Express address books and Eudura address books, but why not ones from Mozilla Thunderbird? LAME! I had to switch to Outlook for business reasons and also so that it syncs better with everything, but this change has been a major PITA, especially considering the move to Thunderbird from Outlook was so easy.
3. Lame Internet Security Warnings every time I open Outlook

Attention Microsoft, this is Captain User Experience calling! Mayday, Mayday! We're going down!
I mean, how hard is it to put a little rule setting check box that says something like "Remember this option for next time"? I realize that common sense isn't a program language, but you'd think it would be a job requirement.
Okay, there is my rant. Feel free to add your own gripes with Outlook.