My Linksys router is pretty good at re-establishing the connection quickly, Linux might not be so good. My friend used to use Linux for PPPoE, and he got a lot of nasty crashes.
WRT-54G is Linux, so that's a pretty bad argument
When I lived in the Fraternity house, I set up a Gentoo box to serve as a gateway/NATing router. Before we spent the money on the dedicated machine, I tried several different flavors of firmware for WRT-54G (we got three of these so we could get WiFi almost everywhere in the house), and none of them could scale to the ~50 computers on the network. They simply didn't have enough ram to persist that many connections.
We also bought two 20-something-port 100MBit/2-port gigabit switches, which we planted in the attic. It took about a month for me and one other person to finish wiring every room (2 singles, 14 doubles, 2 triples). It's been 4 years, and the system only gone down once in that entire time, due to the power going out.
In going with this solution, I realized how crippled these little boxes really are. As switches, they are fine, but the minute you start relying on a limited-RAM machine to perform NAT, you're pretty screwed. Aside from the obvious benefit of not having to reboot the WRTs six times a day, the internet-bound latency dropped significantly, and WiFi connections stopped dropping.
