I use TDOCS ($795) since 2000 with no update but still works beautifully virtually all the time. I also sometime used PerfectByte ($69) since 2006 because some insurance wants a newer ADA form. Patterson bought out TDOCS and offered me their software for free IF ONLY I agree to pay them $3600 for training plus annual recurring fee; I told them 'thanks but no thanks!'
I like them both because they're cheap and extremely easy to use even without training.
My office runs Dentrix with the G4 update. Have it in all 8 ops + hooked up to 6 other terminals in the office. LOVE IT!! Gives me + my partner all the data for practice analysis we could want. Easy to use(even for us docs ) staff loves it, and even patients love it when I can very easily send them and e-mail with an attachment that has their treatment plan and a short video with info about any procedure I'm proposing in the treatment plan through Dentrix's feature called guru. Also has real simple remote access via my blackberry so when I get an emergency call over the weekend, I can very easily get patient chart info or look up my schedule for the next business day to tell the patient when they can come and see me.
Not the cheapest practice management software (ours was about 13k for install/set up/training and 1st years service plan) but for me + my partner and our practice and what we want out of it, it's a great fit!