Bum marketing can definitely pay off, but its quite hit or miss until you get the hang of it. Once you get it down and learn how to write articles that get people to click and that rank high in the SERPs, it is much more profitable. One major benefit of bum/article marketing is that you get hundreds of words to sell your affiliate offer, compared to just a few lines, like with PPC. Combine good articles with a simple landing page and you can make some decent cash.
One tip, if you are outsourcing your articles, remember, you get what you pay for. Cheap writers will usually come up with some shitty ass articles that aren't going to sell your offer.. so if you can, take the time and write some good articles that are tailored to your offer, and if you get a successful article, re-write it like 10 times.