Well, it actually seems to have gotten a lot better in the last few months. Currently, though, it seems to be unable to store flags (except for deleted) on the IMAP server. (Or maybe it does, but it only flushes them on exit?) It uninterruptably downloads the headers for every message every time it opens a mailbox. Searching doesn't seem to happen on the IMAP server, making full text searches impossible. It doesn't seem possible to select a mailbox from the folders list that also serves as a folder. That is, I can have the mailbox imap://imap-server/INBOX/read-mail and the mailbox imap://imap-server/INBOX/read-mail/from-bob. Mutt cannot open the parent folder/mailbox from it's list mode. I can type it in directly, though. (Actually, after further research, it looks like I can't open any mailboxes in list mode on servers that support combined mailboxes and folders, as it thinks that they're all folders.)

On the plus side, they implemented IMAP over SSL, which seems to work quite well. Also, they finally implemented understanding external changes to IMAP mailboxes (where another client accessing the same mailbox changes something), but, apparently, since most flags are not stored on the IMAP server, it may get them wrong when messages are deleted externally.

That's all I can find after about 10 minutes of looking. I'm sure that there are still more problems. I just can't remember what they might be right now. All in all, it's just not ready for prime time. But I think it probably will be, eventually. By the way, most of these problems seem to stem from the fact that it was initially written against the UW-IMAP server, which, for years, supported very few advanced IMAP features. As such, ability to use those features seems not to have been thought of when implementing IMAP support for Mutt. UW-IMAP and Mutt seem to slowly be adding those features, but neither one is there yet.