I left Calgary in the fall of 2003 and returned in the summer of 2006. A few comments which should not be surprising if you're a frequent visitor to this board:
1. City has grown a lot, particularly out in the suburbs. Lots of new houses and new, understaffed commercial developments. Which leads me to number 2:
2. Labour shortages means that many service industries are understaffed (read: crappy service, if you receive any service at all).
3. I would say traffic is worse, but I didn't drive much before 2003 and don't drive much now so it's hard to say. Transit is definitely busy; glad I rarely have to take the C-Train.
Enjoy and welcome back!