I finally read this thread, which mostly happened while I was away on vacation but keep cropping up.
Although this is interesting and intelligent stuff, I'm going to be insufferably arrogant and disagree with the consensus.
The implementation seems too much inspired by the J2EE patterns which I find conceptually unfocused and too obsessed with "clever" object-oriented design. Fowler is much better.
IMHO, the Mapper hierarchy is unnecessary complexity. Better to translate all HTTP requests into object/method calls in a fixed way. That's because it simplifies the Front Controller code itself, but more importantly, because it makes for a more consistent way of using URLs and HTTP requests.
If you want to show a "page", you can easly do it from one of the actions. (BTW, I prefer the term "command". "Action" is ambigous: it it the action of the user or the software?).