I think that the trouble is that when you try to get links fast you accidentaly pick up some shady links too and they might get yourself into trougle in the eyes of Google.
I have been doing blog commenting for my own site and I think I am doing it in pretty fast way. But I my site in just 1 months time is now PR3. I am not sure how does google looking for backlink. An other web client I have is ordering me more then than 2000 do follow blog commenting his site was at pr3 and in 2 months his site is now at pr5.