The AOPA web site (http://tinyurl.com/9lebh) has the clearest explanation of
this change:

"When the FAA issued its final Sport Pilot rule, it quietly removed a
privilege that has existed for years. In the past, pilots could carry
passengers in certain experimental aircraft regardless of whether they held
the appropriate category and class ratings. For example, you could hold a
private pilot certificate with an airplane single-engine land category and
class rating and go out and fly a passenger in an experimental helicopter
with no training required. The FAA cited an increased number of accidents
attributed to a lack of category and class ratings as the reason for the
change."


From the EAA web site (http://tinyurl.com/czojv):

"Pilots who hold a private pilot SEL airplane category and class rating
certificate, and fly a SEL experimental aircraft, no action is required."


Since virtually everyone receives their first certificate after training in
an ASEL aircraft, folks who build Lancairs, RVs, Cozys, etc. should be
unaffected.

Regards,
DJ Molny
Extra 300/L N133DF
Rocky Mountain Aerobatic Club