Assault on 13th Labour - Cross Platform Distributed Computing in .NET

BoingBoing linked to a distributed program attack on an encryption puzzle on Perspex City called Assault on 13th Labour. What caught my eye was the fact that it's a .NET console application which runs on Mac and Linux under Mono as well as Windows under the Microsoft.NET runtime.

A cross platform distributed computing application that's 60K is just plain cool. There's no "Download Windows version here, Mac version here, Linux version here" deal - this is the same EXE running on all three systems, collaborating with a central work dispatcher via webservices. Unlike some other cross platform apps in the past, this thing was a simple unzip / run install, and it's not bogging down my computer.

Could this write once / run anywhere thing actually work?