At one point I was going every 3 months. It really worked--I went from having early-stage gingivitis (measurable pockets) to nice healthy gums and clean teeth.

Then I went down to every 6.
I've been really bad about it since moving here--I finally had it done after 2 years *gulp* Dental care is so bad here though, a standard NHS exam doesn't include X-rays! I had to go private to have the hygienist clean my teeth.
As for bad teeth... all of mine are filled, I have 9 crowns, 7 root canals, 1 apicoectomy, 3 bouts of oral surgery, 7 years of braces and all my wisdom teeth were impacted. All before 30

PS - yes, I brush! it's genetic.