Facebook App was recently upgraded to 1.2 with the release of Froyo 1.2. Shortly after the release of froyo for EVO, fb had put out an updated app 1.3. Lot of people complained about battery drain from fb since it was always "on" due to the partial wake lock. FB issued a statement and released a patch to address this issue so the new app is version 1.3.1.
However, based on some initial reviews most people still say it didn't fix the issue. Others say it has.
Who know who to believe? Is Android 2.2 needed to allow 1.3.1 to work properly? I have no idea. People just see updates and think they should install the latest, thinking its the greatest, but in reality, that is not always the case.