I've been using desktop PCs as home routers (and sometimes work routers) since I first had a network of computers at home in 1996. At the time it was a hand-me-down 386 running Slackware with a 2.0.0 kernel and a couple 10Mbit NICs. Today, it's a Sandybridge running ArchLinux with a couple 1Gbit NICs. Neither being anything special for their time.
It's interesting to see someone compare a PC to an off-the-shelf router. Too bad he didn't throw in an enterprise class router for comparison (and do latency benchmarks).