I've never hit any of the major bugs, but the iOS app is quite glitchy. The unread count never updates if the mailbox is externally modified (e.g. via the web app), sometimes it goes to zero or one. Sometimes my messages simply don't show up.
There was also that whole IMAP data loss issue. Unsure if that ever got resolved.
There was also that whole IMAP data loss issue. Unsure if that ever got resolved.