Having just recently bought a little Z50 for the kids, I started searching the 'net for some information on the little beasties.
Well, I knew that the 150 models were becomming popular, but what do you know, the Z50, XR50 and that sized bike is having a massive resurgence as well!
Check out some of these articles/sites!
http://bbrmotorsports.com/News/CareyH_TWMX.htm
http://bbrmotorsports.com/News/DB_0202.htm
Whew. Sounds like those guys are having way too much fun. Maybe the kids wont get much use out of the little beastie after all ;-)