Large sections of the Wyvern Map Editor Manual were written as a volunteer effort by the Wizard Ender.
Wyvern's original Map Editor was written by Eric Weber in 1997. It was subsequently hacked on and modified over the years by Rhialto, but the basic design and internal architecture (including the Property Editor, which is really pretty neat) is still Eric's.
Dozens of Wizards have devoted their time to creating thousands of intricate maps for Wyvern. Their feedback and care has been instrumental in making the Map Editor a better tool to work with.
For all the bugs and problems with the Map Editor, you can blame Rhialto.
Future Directions: Rhialto is experimenting with an AJAX-based replacement for the Map Editor. That means it would run in any web browser with no downloads required. It would edit maps directly on the server; no uploads necessary. It's a daunting task, and Rhialto only has an hour or two per week to dedicate to it, so he expects it won't be ready until mid-2008 or so. Until then, we hope the current Map Editor will serve your map-making needs.