That really depends on what sort of enviroment you're talking about. In a production environment, the goal is usually to minimise risk as much as possible. Personally, I wouldn't even use Apache2 in production yet, let alone mod_perl2.

Typically, it takes around 1-2 years for a new major version to stablise and properly mature.

The only exception to the above is if the new version does something you really need. Actually, this should really be the only case you ever upgrade to a new version. But it's hard to escape the Microsoft upgrade-everything mindset sometimes.