Yahoo and GMail have notification relay service with RIM, so they notify RIM when new messages arrive and handle them accordingly.

I have been using the default gmail config with the BB for over a year now with great success.

I configured and tested the IMAP setup today and it did not seem to offer much, or enough to overcome the delay in the messages to the BB.

I have reconfig'd back to the original config.

It works, but was a bit slower, if you ask me.