mats do wear out, especially if you use the lines on your mat to measure rather than the markings on your rular. If you use the markings on your mat you over cut on those lines and this means all the wear is concentrated on the lines. then the blade, however sharp, starts skipping from one channel to another. you only have to look at you LQS cutting table to see the mat of many grooves on the yard and half yard lines.
Learn to use your rulars for measuring it will be more accurate
When a mat does come to the end of its life, I switch it to gluey work and use it as a table protector for other crafts. better than using newspaper.
If you get wadding in the cuts there is a mat smoother you can buy which is relitively expensive but a group could buy one between them, and then you can just take your mat to group and clean it up when it needs it.
The heavy duty mats are better but they still do not like direct heat and need to be kept flat as possible. Once warped they are next to useless for cutting as they are actually dangerous.
Becks