My advice… don’t buy into the tagging for Page Rank idea.
Seriously, as soon as serveral hundred people simultaneously start to spam the social bookmarking sites with multiple accounts and trashy results, they’ll start with a rel=nofollow tag. Then they’ll add a Captcha to every bookmark entry form to make the automated software useless. And your $150 will be down the drain without much to show for it.
That’s not to say you shouldn’t use tag and ping. But rather than using tools to abuse the services, find new techniques to use them to build traffic.
In the end, tagging for traffic will outlast tagging for pagerank by a long shot.