coopster - 12:33 pm on Mar 17, 2011 (gmt 0)
The FB developers blog has some info:
However, the key phrase is on this blog post [developers.facebook.com]:
Lastly, we want to be clear that our deprecation of FBML does not impact XFBML, such as the tags that support social plugins.
Some of our supported FB Like boxes were out of commission yesterday for a bit too. I think they botched something in their rollout. They are back up and running now without any changes.