Neither use C2DM though, they use their own solutions and they frankly don't work well. My email is pushed to me within 120 seconds of it appearing in my inbox. I never get Facebook push notifications (I just simply never have, and it is configured properly), the Messages are terribly inconsistent (they appear in the app, the Messenger app, and sometimes my desktop will grab a message and I'm completely unable to access it from either Facebook app). Additionally, Google Voice will received messages, 10, 20 minutes "late", with no explanation or reason.