depends on what you're selling really. If you have a site that targets most of the friends on your list, you will be sitting pretty with some nice traffic that will keep growing as long as the content stays good. And of coursei f you have a nice product thats targeted that will sell like hotcakes too. I'd say very valuable if its targeted.
im planning on selling services within the site.. like bulliten posts, or postings on friends pages..
oh, if that's the case, then yea you could charge pretty good... Maybe charge 5 bucks or so for a bulletin post or something, I think that's a fair price... someone was doing this the other day so you may want to look it up.