I'm sure this question will come up at some point. My opinion: Don't use it. Think about it. I just went through the description of how the AC system works. You take a high-pressure liquid and run it through a small orifice to create a change in pressure and temperature. If you goop that opening up or any of the other small passages in the AC system, you're asking for trouble.
There are no easy fixes with AC. You can't use a Band-Aid when you need surgery. Fix it right, or take it to a professional. It's not likely you'll fix your AC system with stop-leak products. In fact, I believe you run the risk of permanently damaging your AC system. If you do decide to try stop leak in your AC system, make sure you follow the instructions to the letter for best results.