How often should I change the bulb???

Ive been running one of these 125W fluorescent grow bulbs for my clones then veg a month or so. Its been 2 years this month (April) since I bought it. It has a lot of hours on it but still works. Just wondering compared to hps which people like to change every 6 months or year. Any input would be great.

http://www.aquaserene.com/store/products.php?1036&cPath=11

cfl's have 10,000 plus hour ratings(box say anything?) and should hold if not overheated.I would do the math and have a replacement handy just incase.
I forget if they just burn out or slowly fade.Any flickering observed?

Yeah the box says 10k hours. When I bought it the bulb died after one day lol. So I took it back and they replaced it. Just wondering if other people just let them run till they die or change them. It has worked great though I might upgrade to the 200W after this one even though its twice as much 80$. I dont see many people using these.

Does anybody change them after a couple years or just run them till they die?????

you should be fine as loong as it doesnt flicker, make a noise or anything. but i would go ahead and replace it and keep it as a backup. CFL's to deminish light after certain period of time and will continue till they burn out.