qkw02:
Here’s the official word from the FCC:
http://wireless.fcc.gov/services/index.htm?job=service_home&id=general_mobile
and
http://wireless.fcc.gov/services/index.htm?job=service_home&id=family
Here’s the official word from a popular GMRS/FRS radio manufacturer.
This two-way radio operates on GMRS (General Mobile Radio Service) frequencies which require an FCC (Federal Communications Commission) license. A user must be licensed prior to operating on Channels 1 through 7 on high power or 15 through 22, which comprise the GMRS channels of this radio. Serious penalties could result for unlicensed use of GMRS channels, in violation of FCC rules. Operation of this radio is subject to additional rules specified in 47 C.F.R. Part 95.
From this it appears that one should obtain a license if operating on any of the GMRS-only frequencies 15-22, or at more than .5 Watt on any of the GMRS/FRS frequencies 1-7.
Having said that, to the best of my limited knowledge, I’m not aware of any radio that can detect if the operator is “Not Licensed” and, therefore, automatically reduce power on channels 1-7 or automatically prevent one from even operating on channels 15-22 if not licensed. I guess its really just safer to get the license if one owns a radio that is able to communicate on a GMRS frequency. 
Anyone else able to shed more light on this? 