We use a continuous integration server at work (Atlassian Bamboo) which attempts to build the software on all the platforms we are targetting. This is really useful because it prevents us from ignoring a platform for long periods of time. When it tries to build, it will fail and give us an email so that we can then go and do a better job of maintaining the port.
If you are an experienced UNIX/Linux developer, then you probably have a fairly good knowledge of writing portable software anyway to cater for the many different Linux / BSD distributions we use today. Using the Mingw toolchain (and certainly Cygwin) will create a sufficiently UNIX-like development environment for you to work in anyway (Arguably more UNIX-like than Ubuntu ;).