Best thing I ever did for my bottom line was start managing my own billing. 18 years in practice and I have been through three different billing companies - each time had the same experience. Things started out well but then billing started to get sloppy. Eventually patient were mad, I was mad, and accounts receivable was a mess. It seems like the billing companies are competent and willing to collect that first 90% that is easy to collect. The 10% that actually requires some work gets put on the back burner - 10% uncollected over years ends up adding up to a lot.
Last year I decided to bring it in house. I think it is easier to do your own billing now than it used to be. Between Office Ally which makes submitting bills easy, and Google Search which allows you to find out the answer to just about any billing question in a few moments, things are way better now. Granted, you have to have someone reliable on your staff to do the data entry and lick a few envelopes, but I am much happier now, so are my patients, and so is my bank account.
Good luck!