I was using one and it would unlock phone and would start apps. I was at a verizon store yesterday and they said not to use a pouch with a magnetic flap. I bought one for for my droid that had a velcro flap and I haven't had a problem since.I have played with the magnetic pouches and holsters with my Droid. They definitely put it into Car or Multimedia mode. I don't think that part is harmful, however if you jiggle the holster around a little you will see that the Droid moves around enough to cause the Car or Multimedia mode to stop and reactivate which turns the display on - I believe in the long term this will affect battery life.
I haven't found an idea solution yet.