On: Ask HN:How do you use Facebook Pages to promote your Web App?

Maybe you knew this already but if anyone else is reading here is a really simple example of the like to interact code - http://thinkdiff.net/facebook/how-to-detect-fan-of-a-faceboo...

Great link, that really sums it up. A note, though: some people report that fb_sig_is_fan does work. Worth at least trying out before you switch to <fb:visible-to-connection>