If nothing else, I've certainly learned a lot. In addition to the above, it uses Geo::Gpx to do the GPX parsing, JSON to translate between JS & Perl, and draws on a few jQuery plugins (mainly from the UI suite, but also the form plugin and a completely reworked version of jqueryFileTree.
The functionality as it stands is pretty limited - you can upload a GPX file, browse through its tracks, segments & points, see where they are on a map, and edit/move them. Waypoints & routes are not yet supported mainly because I can't get them off my GPS over a simple USB connection, but if all goes well I'll add them in later. And there's a bug/feature list longer than.. uhh.. a really long thing.
But its certainly getting there. And there have been a few useful spin-offs already (I've just released Geo::Google::PolylineEncoder & Test::Approx to CPAN, and I'll try & package up jquery.tree.js & release that too).
Feel free to try it out, and let me know what you think!