I used mason for my own projects and PHP at my day job. What I miss most about mason syntax is being able to layer content and control structures. In PHP, once you open a tag you are writing code until you close it (HEREDOC and NOWDOC being poor exceptions.)

As for a framework (which is another ball of weasels) inheritance from autohandlers in mason makes site structure code re-use dead simple. I assume there is a PHP framework that does something similar, I just haven't looked very hard. Some people like to use mason for rendering/layout inside other frameworks (Catalyst, Bricolage, etc,) so this should be another point to consider.

Multiple inheritance, closures... my list goes on, but that's all more general PHP vs Perl.