Yesterday, the XDA-Developers forums were buzzing with news that Froyo (Android 2.2) had in fact leaked for the Samsung Epic 4G and Samsung Vibrant. Now, before you get too excited about Froyo on the Epic 4G, apparently it is very much not ready for a public release, and is suffering from radio issues and is generally instable.
Froyo for the Vibrant, on the other hand, is reportedly quite stable. Two custom Android 2.2 ROM builds are now available for the Vibrant, which can be found here and here. No word yet on when either will be officially released, so stay tuned for more information as it becomes available.