Source on git now has:
+ different genesis block
+ ridiculously easy minimum proof of work threshold
+ protocol message header bytes are { 0xfa, 0xbf, 0xb5, 0xda } instead of { 0xf9, 0xbe, 0xb4, 0xd9 }
If you compile and connect and turn on coin generation you'll generate a lot of play money quickly...
(I've turned off generation, but will keep my three clients -- two Linux, one Mac -- connected)