RE: Whats been the biggest effect of 2.4 ghz
There is one club in my area that is 2.4GHz only, since it is about 1.6 miles from another (already established) club. Since the new club is 2.4GHz only, no frequency sharing agreement is required.
2.4GHz eliminates the need for frequency pins, and it eliminates most glitches that affect 72MHz systems. The short receiver antennas also make for much cleaner looking installations in the aircraft.