Stock email app: works fine for about a week then stops fetching. Solution: switch to k9 or delete accounts in stock app and redo once/week.
Gmail app: eventually stops syncing/connection problems, possibly due to sending attachments. Solution: go to settings > manage applications > filter > all > gmail storage > delete data
ALSO, "gmail notifier" in the market takes care of gmail not notifying you for every email.
Nothing to do w/ email but my 4th tip is to reboot phone every 3 days if people you call are sometimes complaining about echoing/muffled/garbled voice. You won't get these complaints if you use bluetooth/speakerphone a lot.
All of these bugs have been reported. Verizon/motorola/google should be ashamed of all this fundamental stuff that's broken, but at least there are workarounds, right? I still love my droid & it still kicks iphone butt.