honestly google doesnt really penalize it at all ive built a couple hundred forums with usenet feeds and every one indexes well, and ive gotten up to a pr6 with little effort on one site. so no it doesnt penalize it like they normally do with regular web content.. every forum is different thats how google looks at it. Take a look at hostingforum.ca and look up the keyword hosting forum in google and see what he serps say. powerful tools.