Been running Mail for OS X for a few days last week. I decided to give it a go after seeing my friends use it and.. Oh well. It totally messed up both my personal and corporate accounts, flagging is broken, mark unread too because as soon as you delete one message the next one is automatically read. And I actually had one of our clients reply to my personal e-mail, I wonder how that happened.. Also, my contacts were never imported which is strange.
Anyways, I’m back to using the Gmail web interface for both accounts, multiple sign-on works well and Google can also display popup tooltips when new mail arrives. Hopefully OS X Mail didn’t delete any of my e-mails and contacts on the server ;)