I've been with InCharge now for just under 3 years. I had close to $15 000 in debt. They managed to wipe all my interest rates so I am only paying the principle. For a while I did pay a voluntary donation, but stopped that when times got tough. There was no problem with it.
I have skipped payments a few times when times were tough as well and they were great to work with.
My final payment will be in June 2011 and I can't wait.
Also, it's true about the credit - I saw my score the other day and was shocked. It does help you build credit.