I was recently lucky enough to participate in a multi-player PBEM game organised and umpired by Norm, of Battlefields and Warriors fame. The battle was Germantown, the game published by Decision Games, and the report is up on Norm's blog here.
Before I got into miniatures gaming I was involved in the PBEM Diplomacy scene. It was huge fun, though a little too demanding of time and attention to continue for very long. Norm's game - well conceived and very efficiently run - was a lovely reminder of how enjoyable multi-player PBEM play can be.
If Norm ever runs something similar again, I would advise anyone with the remotest interest in it to jump at the chance to join in.