Ever since I bought the car, which was in August of 2009.
During the 400-grit, there was a LOT of yellow dust flying out from underneath the sander. Lol. So there was definitely a lot of it caked on there. Same with the fogs, but since my headlights were my main concern, and I only had one kit, I wanted to make sure I had enough to get the headlights done. Fogs were just extra.
And there's actually more than enough in the kit to do both headlights and both fogs. I ended up with three 400-grit pads left, two 800-grits, and the one 3000-grit pad is still better than 60% I'd say. Plus the compound pad, which I don't think will really ever wear out. Not for a while at least.
You just have to make sure you hit them with the 400-grit until ALL yellow dusts stops. And keep watching the lens. If you see spots that still have the haze to them, keep at it. And it doesn't look like much until after the compound and a wash. That's really what does it. When I got done with the 3000-grit I wasn't very impressed. But then I hit it with the compound, then hit it with the 3000-grit again, and then the compound again, and then I washed it. After I dried all the lenses with a towel (after the wash) I stood back and was like "Wow.."
Another tip, when using the sanding pads, make sure to periodically wipe off both the pads and the lenses to help the pads last longer. Also, wiping off the lenses will give you a better idea of what areas need to get hit again.