Just a quick post – While using the Internet Sharing function of OSX, I ran into some errors where my client machine wasn’t getting an IP address. I did some digging, and it turns out that the dhcp lease file is stored at this location:

/private/var/db/dhcpd_leases

This is definitely the location for Lion – I’d imagine that it’s the same for 10.5 (Leopard) and 10.6 (Snow Leopard) as well… although i’m not 100% sure. I fixed my issue with clients not recieving IP addresses by deleting this file – I’m not sure if that is a good thing to do, but it worked for me! It was interesting to see who had connected when I accidentally set it to an open network, too… “Andy’s iPhone”, I’m keeping an eye out for you!