Facebook has created a pretty slick javascript API that allows you to add Like buttons, Login buttons, and more. Yet there is one major problem with the force.com platform. This requires you to use custom facebook tags such as:

<fb:like href="http://developers.facebook.com/" width="450" height="80"/>

But when you try to save the page the Visualforce compilers interprets "<fb:" as the markup for a Visualforce component and throws an error:

Error: Unknown component fb:like

This makes it a pain to integrate force.com sites with facebook. This is actually a Visualforce issue but the really loser here is force.com sites and this is why I posted in the sites section.

Thanks,

Jason