For organized rides it really should be posted wherever the ride is posted, web, lbs signs, etc., that helmets are required and ipods are prohibited. I would hazard a guess that if someone showed up for a ride without a helmet, someone would speak up.
They also may make your pacemaker malfunction:
http://news.yahoo.com/s/nm/20070510/...art_ipods_dc_3
Sarah
When it's easy, ride hard; when it's hard, ride easy.
2011 Volagi Liscio
2010 Pegoretti Love #3 "Manovelo"
2011 Mercian Vincitore Special
2003 Eddy Merckx Team SC - stolen
2001 Colnago Ovalmaster Stars and Stripes