they do dry out, get brittle to the point they will almost snap in half. Lots of cut lines showing and your cutter will skip and you have those little threads that didn't get cut. I have started writting the date on all my new ones. They do wear out, and will dull your rotart blade. Mine are used ALOT so that may explain my take that they do wear out. I wait for 40% off sales or coupons.
Just purchased a Fiskers and LOVE it so far, blade seems to glide over it. Will have to see how it holds up, AND it is reversable with lines:)