I've seen a lot of XS modules that skimped on docs because they thought they could, when in reality, the syntax can and might be different. Try googling for info on OpenGL.pm and you won't find much, and the POD doesn't help either... so where, oh where, is that canonical spinning Gouraud shaded cube in Perl? I certaintly can't find it. So, even to this day, I haven't used OpenGL.pm

Bottom line, documentation is great stuff, and if you can take an extra 30 minutes and include a simple example with that XS module, I'll thank you for it! :)

Even if you're own module is not XS-only, and you just have an API, a few lines of code using that API is always useful as well. Another bad habit I've seen is CPAN pages that say "for documentation visit http://xxx.yyy.zz, which is a problem because then your handy perldoc in an xterm is suddenly no good.