Gmail app on LG Optimus U doesn't get email anymore
I've had this problem before.  Sometimes the "unread" count goes up as well, but the emails never show in the Inbox.

The best thing to do to fix it is to go to Settings -&gt; Applications -&gt; Manage applications and clear the data for Gmail and for Gmail Storage, then to try syncing your Gmail account again.  If this doesn't work I recommend clearing the data for all Google apps -- Gmail, Talk, Voice, Google Framework Services, etc. -- then rebooting and trying to sync your account again.