I use 5.8.5 on Win32, as it was the version that I most recently compiled to test out the free MSVC7 toolset.

On the Debian box, I have 5.6.1 (the stock Debian Perl), to run apt-get, 5.8.0 for testing and 5.8.4 for my scripts.

At work, I have the IndigoPerl 5.6.1 release and a copy of a self-compiled 5.8.2 for Win32, and 5.005_03 for Solaris, because it is there. I don't have the permissions or inclination to upgrade the Solaris Perl at work, as I use it there mostly as better awk / sed combo.