I switched back to the iPhone in March. I had been using gmail for over a year with android with no issues. After setting up gmail on the iPhone using exchange, emails were not being pushed to my device, I did not get instant push notification. Most often than not, email push notification was delayed 15-20 minutes.
The only way to get gmail email was to go directly into the iPhone email app. I did some searching over at the gmail support site, other sites and found this issue. It appears that there were quite a few users who experienced this problem. It didn't matter what you did as the end user (delete account, recreate the account, etc.), the issue persisted. Some users reported that the when they tried to logged in or were logged in the password was incorrect. Nobody was certain whether it was an iOS issue or a gmail problem.
I don't know how wide spread the problem is or was. What I do know is for that time period listed above, gmail wasn't working for me. I signed up for hotmail during this time, since hotmail not supports exchange. About a week after that, gmail started working again.
So the basic problem was that there was no push. Emails sent to gmail weren't coming thru unless you did a manual refresh. That link in the first post about how to setup gmail on your iOS device seemed to be the only answer, but most everyone had it setup like that to begin with.
Many people had no issues at all or didn't know they did or didn't setup gmail thru exchange or had gmail setup thru the stock email app using IMAP. Who the hell knows.
I could list links to google that show the problem, but it's pointless. It';s working again for me. But when I see posts like this, it doesn't surprise me.