Google officially announces OAuth support for IMAP/SMTP Gmail
googlecode.blogspot.com
googlecode.blogspot.com
http://web.mailana.com/labs/handmadeimap/gmailoauthexample/i...
http://github.com/petewarden/handmadeimap
There's now also official code in several languages available at http://code.google.com/apis/gmail/oauth/code.html
And based on my experience working on Syphir (https://www.syphir.com), chances are you won't run into any IMAP throttling problems based the frequency of your access. Syphir makes a few IMAP calls per user per incoming email, and we generally haven't run into any problems.
http://benmetcalfe.com/blog/2009/10/my-gmail-password-scares...
It will be interesting to see how successful adoption of IMAP-via-OAuth will be.