Don't know how long they should last but I know mine needs replacing. Got it at JoAnne's back in 2005 and it has lots of cuts in it. I picked up a rotating mat with a self-healing mat and I love it. Found a site that will cut to fit whatever size you want/need and its self-healing. They come in either with or without the markings. They will also send you the leftover pieces they cut off as they start with a certain size and cut down to whatever you ask them to. Hopefully this will be my last one.
Suz in Iowa