The thing is, 20 years ago maybe you developed on a Sun box, then the guy down the hall tried to compile it on his HP machine and it crapped itself because of some Sun-related assumption you made in setting things up. Then you mail it to a colleague across the state and he compiles it on OSF/1, hurrah!

But now, people write Linux libraries, tested on a Linux box, for people running Linux, and only compiled on Linux. There may be OS X support. That's it. This is not the 1980s, where 10,000 Unixes bloomed. With 4 Makefiles, you could support Linux, OS X, Windows, and FreeBSD, and thus cover 99% of your audience. I'm sick of watching configure scripts take longer to run than the actual compilation.