I have had it for about 10 years. However, I have successfully kept it to a minimum. I have a desk job and have a golf bal and a tennis ball under my desk. I run my foot over it basically all day. I probably spend at least an active hour each day on the ball. It feels great!
The only time it REALLY flares up is when I do a ton of walking...I'm going to Disney at the end of the month and I know that it is going to kill me. Oddly the running is not as hard on it as the walking. probably because I walk in less than ideal shoes and wear great (and very supportive) running shoes.