I did some quick research - here is a copy of a post from Jeff Myers (SEFF).
SEFF will have some rules next year (2011) regarding 2.4 systems at SEFF.
1. Pilots will only be allowed to operate radios when located at a pilot station. There will be 26 pilot stations at SEFF 2011.....just like we had in 2010.
2. If a pilot needs to check their radio system when not at a pilot station they must hardwire their transmitters to their receivers with an appropriate cable.
3. For those that don't have the ability to do this, we will have a few designated locations behind the flightline boss EZ Ups for pilots to turn on a 2.4 radio to check something out.
4. My staff will need to discuss FPV and other 2.4 video and photo systems. They may not be allowed next year. I need to do some more research on the technology before we come up with any rules on this.
5. Above rules will be in effect from 7 am to 9 pm. We did not hear of any reported problems after hours. As long as we are not having problems at night, we so no need to impose the rule after hours.
Anyone found breaking these rules will face significant consequences. The penalty will be severe enough to deter those that are prone to breaking the rules.
It never fails....just when we think we have anticipated everything and have the event nailed....new things come up. We know all the major radio systems are solid products. We don't know how they all work together at a large event like SEFF. It is safe to assume that at times....well over 85 radios were on at one time. We did have enough people report "lock outs" / "complete loss of control" to where we know that it is prudent to make some changes before someone gets hurt.
We work very hard to make SEFF the best flight festival anyone could ever attend. We want to make sure we keep it that way. It is important that every pilot that attends SEFF feel comfortable to fly any electric aircraft they own. We have a year to plan 2011 and may come up with better solutions so understand that this may be fluid.
I thought most of the bigger events were doing something similar.