I have nothing to add but a +1, sorry...

N9 has repeatedly stopped updating gmail for a while now, sucks really bad.

Update: i just noticed something strange:

Some of the emails (i'm using threaded view) showed the same (wrong) subject line, which was the subject of one particular older e-mail. I manually deleted that particular e-mail in the normal gmail on my computer, pushed the refresh button on my N9 and it started syncing normally again.

No idea what happened there...