Canon service has been VERY IMPRESSIVE for me.
I once dropped a 10-22 on a 40D. You know, those lenses are supposed to be "borken" to avoid harming the mount as well, and the lens was broken into 2 pieces. So I sent in the 2 piece of 10-22, and got it all fixed with 85+10 shipping, plust 20% discount with CPS.
Not only they fixed it, changed USM, some cables, electronic panels, but they gave it a completely changed barrel. The nicks on the barrel are all gone. the lens is like new, and I only know it's not because it still get the same small nick on the rear element. Lord it smells like a new lens...all these for only $80.
I also once bought a 28-300 from a guy. the lens came in stating "no problemo" but a little nick on the barrel. I wasn't able to touch the lens until 60 days after it mailed to me, being away for about 2 monthes. It made a squeaking sound when zooming. I thought it was no big deal but since it's still in warranty I sent it in.
I was a little suprised to find a invoice came to me after a few days. I called in and they said no receipt was found. Well I then faxed in the receipt and no more questions were asked.
When the lens get back, the paper work reads "changed IS assembly, USM assembly, bla and bla". WOW, I didn't know that! It obviously shouldn't be a in warranty service since I belive all these problems are caused by a hit-on-the-rock or something, whch also made that nick on the barrel. But they fixed it for free anyways!