I've been racing some Reynolds dv46t's and noticed a lip on the braking surface and some shiny patches (glazing). what amount of wear is normal in a season of use? what kind of wear is everyone else getting? I've been using TRP's carbon pads but switched over to Swiss Stop yellows after I noticed the wear.
For cross it is much more dependent on the mud/dirt conditions you ride in than brake pads. Carbon rims are definately not designed to be used in muddy conditions and will get destroyed quickly. Carbon and abrasive mud don't mix very well. If you have an alloy wheelset, run them in the mud fests. The extra weight won't really matter when your bike has 10 lbs of mud packed in it.
When you start going through multiple layers of carbon, it will begin to delaminate and the rim can fail. When? That all depends on how thick your specific carbon rim section is. Just keep and eye on it. If you can push on the rim sidewall and hear a cracking sound, that is odviously not good. If the braking groove gets deep enough that you can see the individual layers, that is not good.
I have yet to do a mud race in the 3 years I have been cross racing, so my rims are pristine.
Just don't use your brakes and they will last forever!