Wil Shipley says charge for upgrades: http://www.viddler.com/explore/rentzsch/videos/4/ (He is the dev of the OS X app, Delicious Library.)

I would say that not charging for major upgrades impairs developer-customer relations. Without upgrades, the dev has an incentive to stop working on their app and write a new one (and thus get a bunch more money).

I can't think of any well-known piece of Mac shareware that doesn't charge for x.0.0 upgrades.