Not having ever done so myself, PBEM or Online suggests alot of advantages to me.
1. Players don't have to wait patiently while the GM fumbles with the rulebooks.
2. In PBEM personal schedules are much less of an issue
3. GM can commumicate privately with certain players with out the others knowing, So that players can have secrets from other players. i.e. Player X is a double agent or stoolie.
Because I would have such a difficult time setting aside a day for rpgs, a play by mail campaign sounds perfect to me. BTW, I have be surveiling Travelogue2, interesting.