in reply to Idea for Perl Learning Tool
I don't know of any existing tools like this.
However, there is a really cool toolkit for doing regular expressions in the new ActiveState Komodo interface. You can type in a regexp and some text to match. It highlights what is currently being matched and explains what is going on in English. You can advance through each part of it and it shows what is getting stored in each of the variables $1, $2 etc.
This might at least help with one aspect of perl although a general tool might be a great learning aid as you mention.