Crab,
I have 2 VHF and 2 FM in the a/c. Most of the the time I am too busy to tune to 121.5. If I am going a long ways on a x/c I'll listen. But GA CTA airspace and Air to Air Vctor take the priority.
What is intersting is that the US Foreast and Park Service require and FM air Guard freq on all contract aircraft. This has come in handy a bunch. For example: You arrive on scence for a resuce or a fire and the ranger or the fire crew does not have the air to ground fm , they can always come up on the Guard freq that overides the the fm and make contact, then switch.
RB