Last night I released Devel::CheckOS and Devel::AssertOS. They are a wrapper around $^O with some extra functionality. For example, where you can check $^O's value to see if you're running on a Linux system, you can use these modules to check for OS 'families' as well, such as whether you're running on a Unix system.
Devel::CheckOS provides functions which return true or false depending on whether there's a match. Devel::AssertOS dies when you try to use it if there's no match.
The intention is that authors will use these modules whenever they write platform-specific code so that it will die with an appropriate message, which will be picked up by CPAN testers, and make them SHUT THE HELL UP when they try to do stupid things like test Solaris::Foo on Linux or VMS::Bar on Windows.