So far we have done our marketing ourselves and it is definitely slow going! We have a very small marketing/advertising budget, so there wasn't much of a decision process.
On the plus side, it is extremely rewarding when a marketing effort pays off and you know you have done it all on your own! The negative would be that it takes time (which I don't have much of) and a lot of research (and lessons learned) to find the best ways to do it on your own!
I still have a marketing firm on my list of things that I would love to implement when my budget grows!!