No, I haven't had any problems with nicks in my rotary blades. I do try to ALWAYS close the cutter whenever I put it down - one of those things I'm pretty obsessive about after I picked one up by the open blade! Just ask any of my quilting classmates - I always tell them they owe me 50 cents if they put their cutters down open! lol
I cut anywhere from 4 to 8 layers at a time, and when I notice that I'm having to really put a LOT of effort into cutting, I change blades. Also, depending on the fabric, I check to make sure the cutter isn't full of lint & that the blade is snug, but still rolls freely.
Hope that helps.
sue