My main Perl project is the software construction tool Cons. As we're making it a point to support Cons under multiple Perl versions, I regularly run our regression tests against 5.00307, 5.00405, 5.00556 and 5.6.0. (I'd like to run it against 5.002xx as well, but I can't track down a copy; anyone out there have an archive?)

I'll always upgrade to the latest Perl version to make sure Cons still works on the latest and greatest. I also try to use the latest as my default for general work.

We're being anal about making sure Cons runs under these older versions of Perl out of the same concerns about people not upgrading their Perl versions. The reality, though, is that a lot of people can't control when they upgrade Perl; their administrators (employers) decide for them. Consequently, if you're trying to write something that's as easy as possible for as many people as possible to use easily, you need to avoid some of the cutting-edge features that aren't supported in earlier versions...