Exchange/MAPI on the other hand always seems to support push mail. IMAP IDLE exists but many clients do not provide support for it, for example Mail.app for iOS. And if you use Gmail on a few devices via IMAP, you easily run into the annoying 'too many simultaneous connections' issue.

(I use IMAP nevertheless since Exchange/MAPI has some annoying issues on iOS if used with Gmail and Exchange/MAP is not supported by Mail.app on OS X.)