My problems come from the fact that Gmail has been using the POP (Post Office Protocol) for accessing email outside of their Web client. POP is lame if you check the same email account on multiple devices. The Emails are downloaded onto the device that checked the mail. Copies of sent and received emails end up in your inbox and read emails aren’t synced to the server, so if left unchecked the number of unread emails in the Gmail boxes on your iPhone grows rapidly. It got very confusing when responding to emails on the go also.
Recently Gmail opened up IMAP (Internet Message Access Protocol) to their users. IMAP keeps your devices, computers, and Gmail all in sync! If you send an email from your iPhone, it will be in the sent box of all your other devices, read something, its marked as read in all the other devices. It’s the ultimate in email protocols. Trust me, once you’ve gone IMAP, there’s no going back!
To get your iPhone hooked up with Gmail, Google has released some instructions (http://mail.google.com/support/bin/answer.py?hl=en&answer=77702), and a youtube video