I had quite a bit of trouble getting this to work the other day. After some googling I came across this thread over on 6200networks.com. I had matched up the config he had listed just by chance because I was also enabling an L2L VPN. However, I still couldn't get it to work. The trick was to change the IPSEC transform set to AES-256. After that it was smooth sailing. I posted a comment over there but he hasn't approved it yet.
I've discovered ISAKMP profiles too. Very cool!