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?).