I have the Droid X which worked fine until today. I tried the suggestion of clearing all the cache, data and defaults and that did not help. I can open the gmail app and see my emails and even open an email if I am fast enough. Once I scroll down my list of emails or even I don't scroll, it will eventually close. I don't receive an error notice. Sometimes it says connection failed. But all other email clients and even google talk works. I powered down, changed my sync days to 1, and did a battery pull. I don't understand why it just stopped working.
Clearing Gmail storage data always seemed to work, but on the droid x it seems to be a problem with the app...I see quite a few droid x owners saying the gmail app force closes/won't let them see their mail.
See here for more frustrated droid x gmail app users: