I got an email from Warren early this morning with the subject line "google testing imap?". I went right for this message, as there are not many subject lines that could trump this one -- maybe just "URGENT: Server on Fire" or "Free Food Today."
It appears that Google has added IMAP help docs, but the feature is not yet available in my GMail account. Download Squad has a story on this saying that some users can see the IMAP controls already. I will be checking compulsively until I can see the settings in my account and test them out! If anyone already has them and decides to test them out, please let me know how it goes!
I would be really interested to see how conversations and tagging are handled, not to mention that one of the pillars of IMAP is the ability to manage server-side folders; GMail does not support the use of folders.
Anyway, this is great news and I can't wait to see how it unfolds. If you have more information on this, please send!