I constantly see them on the forums when I click who's online. What exactly are they?

I think Batleth explains it best in this thread (http://www.vmkforums.com/forums/showthread.php?t=130788) :)

Search engines send out bots to bookmark pages on websites. A yahoo slurp spider is one sent from yahoo search engine.

Its a spide that slurps people up and eats them... No..

Thanks topaz for the link!