I had a space with Myspace set up for cross-selling and higher search engine placement..but <rolling eyes> with the exception of five kids that are friends of my children, the only other persons that wanted to add me as a contact were males looking for "other" interests besides online selling. (if you catch my drift)
I do have my Yahoo 360 and my MSN spaces.
Both of the above have blogs and those are now being found in searches so if you use key words in your blogs..you'll get picked up. If you'd like to join my 360 feel free to ask.
I can't say if they help or not, but it's just more ways I have of getting myself into the search engines.
As far as message boards? If this message board weren't here, I wouldn't have bought from several sellers. Great advertising along with picking one anothers brains.