Holsters And Accidental Discharges: When using a holster with your handgun it's a good idea to make sure that the opening is stiff and there is no soft, flexible material that can get into the trigger guard. There have been a couple of reports over the last year or so of gun owners using worn holsters or inexpensive universal holsters that are too soft and flexible. Some of those gun owners that had accidental discharges were decent enough to post information about the cause.
If any material gets into the trigger guard you may find that the trigger is pressed while you're trying to seat the handgun into the holster. This is especially true with handguns that have short trigger pulls and no manual safeties (Glocks, XD's, XDM's, etc).
So long story short...if you're using a nylon, leather, etc. holster then make sure that the opening is reinforced with extra material and still retains it's stiffness.