Joe Kissell, author of Take Control of Apple Mail in Tiger and senior editor for TidBits 
, has written a piece for MacWorld on the advantages of IMAP .
He outlines how the IMAP protocol is better than POP, although he notes some drawbacks too (account quotas, very slow with Apple Mail over dial-up).
Instructions are provided on switching Mail.app and Entourage over to IMAP accounts. Joe also offers some tips for IMAP users, including the thorny issue of whether to sync changed mailboxes automatically or not.
One little note from your local IMAP-hater: his article isn’t really praising IMAP-the-protocol, it’s praising the idea of leaving mail on the server. The protocol itself isn’t discussed – this is all user-level stuff.
From a user perspective, would you hate IMAP any less if client/server implementations were better? :-)
[...] Not long ago Mail.app guru Joe Kissell was singing the praises of IMAP for email. [...]
Though, from a user point of view, if you store your IMAP account on a provider server, the problem is that most of time, there will be a quota, which will not allow you to store all emails of your life, then, will make it less easy to use than POP3 retrevial since you’ll have to manage disk space.
For my personal experience, I use an IMAP server at home on my own server, which is accessible from the internet, so that I can get rid of the quota problem.
From the protocol point of view (then, developer point of view), for a client, you can use existing IMAP libraries that will do the parsing for you. You you develop a server, that is still a different story …