"friends" on myspace and facebook are a joke! I have a page on both. I have three on facebook, simply because I want my "real" friends as opposed to the nonsense of having a friend I have never spoken to before, or met, or have anything in common other than being on the same social site. As for myspace, I use it for music and have about 50 "friends".
Like Alan stated, it really is a non-story.
However, lets answer part one of your original question. oops, I can't as I have no idea as to why payed up lib dems don't bother with this site. May be it is because they had a look as saw how boring it has become over the past couple of years?