ORIGINAL: JohnW
2.4GHz jamming devices and any others like it are most definitely illegal to use in the US. The typical fine starts at $10,000 and goes up from there, and I personally know that users of the devices are caught and indeed fined the $10,000+. Regardless, I really see it as a moot issue and not justification for not moving to 2.4GHz. I believe it is only a matter of time before we lose the 72MHz band.
If one wanted to jam your system on 72mhz all they would need is another transmitter that you could get at a swap meet for practically nothing. Then they would probably not be fined.