I've only used this mat less than a week and already there are divots in the mat from my chair wheels. I say "wheels" because my chair is a standard swivel office chair by which the wheels aren't always in the same position versus legs of a stationary chair. Not cool.
The mat is perfect in size but too thin to provide adequate support for the desk chair when occupied. Ruts occur under the rollers of the chair and make it difficult to move easily. A heavier thicker version would be much better.