Well, for me there were a few advantages for my home LAN. One was I had lots of bits lying about, so it cost me nothing except my time.

Another is I can have a DMZ network to put web/mail/ftp servers on, and keep the potential nasties outa my LAN. And I can tweak the router so it behaves as I want it, with more customisation that I'd get from a hardware router (eg firewall rules, logging, intrusion detection, internet filtering).
Oh, and to top it all off, I get to learn more about how networks, firewall, routers and other stuff works!
Neato, IMO.
I use
IPCop, BTW.
Cheers
Mick