With more and more Social Bookmark sites using the rel="nofollow" convention after links it begs the question how vaild and useful are some of these Sites anyway?

Bearing in mind the whole sales pitch of the "Tag and Ping" Brigade was to get more and more links tagged on these directories, get them pinged and thus get Googlebot, msnbot and slurp to index the links and reflect back on the "linked to" site as inbound links creating "authority" sites etc.

With most sites now using these rel="nofollow" commands how can this system work?

If, the other side of posting to Bookmark directories was to get Human traffic then great and the the inbound relevant link effect that accrued as a by product of this then fine.

It seems to be that with rel="nofollow" the inbound link issue is now open to question?

Anyone got any views?

Patrick