I just transferred from Thunderbird with two IMAP accounts and a lot of local folders. The folders came in, but many have added numbers after the folder names. Easy to edit out but very annoying.
Second, the Contacts imported but NOT the contact groups. Why not? I assume I can export those groups as ICS and import but have not tried yet.
Finally, support for a tabbed window would be nice. IE multiple open messages in tabs rather than separate windows.