Gmail Sync going bad on your Apple iPhone is apparently an issue with Google Datacenter. Apparently Google is facing an extended issue with one of its Datacenter and this has affected Push Service for Gmail on the iPhone, Windows Mobile and Symbian S60 platform (you may note that Android, Blackberry etc are unaffected by this). Here, is what Google says in an online forum:
Google Sync is undergoing some difficulties due to an extended problem with one of our datacenters. This has been going on over the weekend, but it’s got significantly worse today, so I’m just letting everyone know what’s happening.
Users can rest assured that Google and Apple would figure out the settings amongst themselves and restart the service.