Among bug fixes on the upgrade, one will improve the function of the phone's GPS. And besides being able to support Adobe Flash, the Froyo upgrade will allow Samsung Epic 4G users to store certain apps on a microSDcard, freeing up some space on the handset.
If your Epic 4G does not show the upgrade at 9:01 pm PST, don't panic or call Sprint. Android 2.2.1 will be rolling out to the device over a 4 day period.