Hello there....... what about get links from social bookmarking?

I have already tons of directory (done them by myself) but I have not yet a social bookmarking exposure.... so in order to diversificate..... I'm thinking to purchase some kg of social :-)

Basically I was thinking to pay a company (not so much) to make manually some social bookmarking for me...it is a good idea?
It will positively affect my pr and serp and visits?
Any bad things can happen?