Like many Perl programmers, I've kept at my "comfortable" level of Perl for a long time. This is partly just not wanting to upgrade, but it's also partly because I want to ensure that code I release to the CPAN works for versions of Perl that most people have installed (which is why I don't worry about 5.005 support that much). However, there are many reasons to switch to 5.10.
But my real reason? Snow Leopard. When I upgraded to Snow Leopard, my system somehow got horribly corrupted. I managed to rebuild my 5.10 installation, but 5.8 wouldn't work because Compress::Raw::Zlib wouldn't work. Once I installed that manually, I found that CPAN wouldn't work because it requires Mac::Files, part of the Mac::Carbon distribution.
Mac::Carbon doesn't install on Snow Leopard with 64-bit Perl. In fact, in going through Pudge's blog entries on this topic, none of the various techniques I tried worked. Lots of google hits related to this, but I found no solutions. I finally gave up and switched to 5.10. All because of one critical module. Maybe this isn't a bad thing?
(Of course, it was real fun to discover that Mac Ports added a new PATH= line to my