I’ve had a problem with my G1 for the past week or two and today I found a solution. My Gmail wouldn’t sync with the device in the same way that it had before. It seemed to be stuck in the past and I couldn’t send or receive any new email using the Gmail app. There was always a big button at the end of my inbox saying “No Conection” with a “Retry” button that didn’t seem to help.
Today I found the solution for the problem on the Google help pages, via the androidcommunity site, and it simply involves clearing the app’s storage.