If its Brazillian hot sex stuff its become quite common on Orkut as well over the last few months. They have moved to captchas but that only eliminates the problem when they are submitting stuff via scripts. Not when they are paying someone in LDC very low wages to advertise something.
One ultimately has to move to a moderator or user-voted on system. Slashdot has had this for years -- the crappy posts get moderated down and one just views the stream 1 level above the garbage level to only have to view things of use vs. time wasters. One would suppose given the history of Usenet News (which is 27 years old and suffered from SPADvertising to the point of being useless on all unmoderated forums) that developers of open forums would have learned something by now. But *noooo...*. As Forrest would say "Stupid is as stupid does."