Have you seen the new Daylite?!

http://www.marketcircle.com/daylite

Dear God!

There is no way you couldn't do a bulletproof GTD in DayLite. The only reason I haven't been using it full time is because I can't figure out good and reliable ways to sync things back and forth to a mobile device out of it.

It is probably complete overkill for a lot of people, but if you want a nice CRM that manages workflow for you, its definatly worth a look. The newest version is hitting beta cycles now and its really quite impressive.