As a complement to my post about FB.ui undocumented hard limit, here are some other parts that should be in the documentation.
Custom html tag
You have to add xmlns:fb="http://www.facebook.com/2008/fbml" xmlns:og="http://opengraphprotocol.org/schema/" to your main <html> element.
If you don't, the <fb:like> (and possibly other <fb:*> elements) won't work in IE. I guess those unorthodox tags won't be interpreted by IE until you define the correct xmlns.
Adding a #fb-root
You also have to add a <div id="fb-root"></div> in your html code. I guess the Javascript API use it for some stuff, but I don't really know why.
The Javascript SDK logs an error message asking for this missing element if you don't have it.
