The Cricut Electronic Die Cutting Machine uses a slightly adhesive mat to cut paper.  The paper adheres to the mat that holds it in place while it is being cut.  This adhesive surface will be reduced over time with use.  A few steps to care for this mat can extend its life and usefulness.

1. Keep them clean.  Remove all little scraps of paper after you are finished.  Using a small spatula or kitchen scraper can work well for this.  Put the plastic cover back on the mat when it is not in use.  Some people recommend cleaning the mat periodically with baby wipes to help restore the tackiness.  I have found this is helpful and really helps to keep them clean as well.  Keeping the mat dust and lint free is a big help in making them last.
2. Don't use more pressure than you need.  There is a pressure adjustment on the blade.  It is very simple to adjust, you just turn it and it has numbers on it to let you know what the setting is.  If your paper is thinner and the pressure is too high,  your paper will tear.  Using too much pressure for thinner papers will also result in cuts in your mat.
3. Some people use a re-positionable adhesive spray when the mat begins to lose tackiness.  If you do this, put a thin strip of paper over each edge where the mat goes under the roller bars.  This will keep the adhesive gunk from collecting on the roller bars.
4. Place your paper on different parts of the mat.  If you are using smaller pieces of paper you can easily position the blade simply by pressing a button, so move your paper around on the mat.  This will allow different parts of the mat to get equal usage.

Expect to replace your mats periodically.  How frequently will depend upon how much cutting you are doing.  By watching the local craft stores for sales, and prices on eBay, you should be able to find mats for a relatively inexpensive price.  Proper care and maintenance of your mats should enable you to purchase your mats when the time is best for you so you can shop for the perfect price!