Why limit your self? I try to do as much link building as I can myself. But time is a commodity, so I also outsource link building and purchase individual high PR links as well.
I'll just do it myself since I am full time blogger. Besides even the top dogs of the blogging world is taking some of their time to do their own SEO.
hmmm it all matters how good you are. My friend gets backlinks by playing world of warcraft. He plays wow, writes guides on the quests and stuff which earn him NATURAL links. Then with the gold he makes, he buys backlinks. I am not saying you should do that, but it all demands on the time you have, and if it is worth your time.
If you have time then make schedule and follow it daily, else hire someone who is cheap and efficient.
I pay for dir submissions but do everthing else myself. I wish I could find a QUALITY + Cheap link building service for the rest though.