In the past few days, many users of the iPhone and Gmail Push service through active sync have been reporting that it is not working. A large Google Mobile Help thread has dozens of posts from unhappy Gmail users.
Google confirmed the issue and blamed the iPhone OS 3.1.2 build, which was out just about a month ago. So I am not sure why people are beginning to complain now.
Robin from the Google Mobile team confirmed the issue and wrote a few responses in the thread. They include:
We're aware of some issues with Gmail sync and are working to resolve them. OS v. 3.1.2 has broken a few things on our build, and we've also had a bug with certain formatting characters in email that has caused sync to stop altogether. We're working on to get a fix out for these items first, and can then start troubleshooting other possible causes.
While 3.1.2 has been a source of problems, there are a few issues across other platforms and OS version as well that we're working on. A number of bugs have been fixed over the past month, so it's unlikely that the source of your problems then is the same as it is now. Also, many folks have been able to sync just fine - sometimes it's a matter of sorting out setup issues and other device-specific variables. We're trying to fix the main bugs that we know about first and then can dive into the 1:1 troubleshooting.
Andrew554321, I did want to address your question about Google Apps. Push email is not currently covered by the Google Apps Premier Edition SLA: http://www.google.com/a/help/intl/en/admins/sla.html
While we do apologize for any disruption, please keep in mind that this is a Beta product that was just recently released; you are of course welcome to go back to IMAP or however you were checking your Gmail before implementing Google Sync. Otherwise, we hope you'll stick with us as we are actively trying to resolve these issues!
Yes, Google Sync uses Microsoft's Mail for Exchange, which is a separate protocol from IMAP and will thus behave differently. There's no link between these services, other than the fact that they can both access your Gmail and that Google doesn't control the protocal for either of them :P
So, if you pay for the Google Apps premier, you are out of luck. Gmail push for the iPhone is a beta product and is thus not covered.
Forum discussion at Google Mobile Help.