About a day and a half ago people, including me, started getting the following error on their android devices when trying to use the Facebook App:

AN ERROR HAS OCCURRED WHILE FETCHING DATA (NULL)

Not very helpful if you ask me.  Parts of the applications still seem to randomly work, such as notifications and widget updates.

The best guess right now is that it is related to the privacy changes they are trying to implement.  While not the first time Facebook has had issues it is still a bit annoying with the recent release of the Incredible adding more Android users every day.
For now, just hang on and wait for Facebook to work out their issues.  There are a few places you can visit to see if their are any updates.

Here is a thread on Facebook about the event.

The Facebook Mobile web page is still working for all your social networking needs.

Update: As of Friday morning it appears that the Android app is now working again. The fix is slow to get out so give it a few hours to get to you.