Hardly ever, really. I'll buy a 100 pack when they are on sale real cheap.... but they rarely ever get used. I'll use a cd-r maybe once every couple months, same with a dvd-r. I never really have the need for them.
I don't spend nearly that many either. I usually prefer making an image of whatever I need and then put it on my iPod or another ext. hard drive. I only burn discs if I need to give it to someone else, or if I back up things.
i don't use many at all. a dvd every now and then to back-up my purchased music, a few dvd's for tivo'd stuff i want to watch on a plane or something. maybe 10 in a year?