I was cursing Google until I finally got the IMAP pushed to my account for them taking so long to do it (I've been a gmail user since the very first beta days, you would think they'd throw me a bone). However now that I've got it, OMFG, I love it. I do with it would push, but having IMAP is such a huge improvement over POP.
Yahoo push is flaky. It works once in a while, but most of the time I get the email within 1hr or 3hrs. Google is good, but I would like to see push gmail. True push is like blackberry. get your email within 1 minute.