I second pretty much all the reasoning of the previous posters. I've got to say, though, we don't feel like we're "tied to Disney". We feel like we've got 8 lovely resorts we can vacation at... and with some of them there are theme parks (if we want them).
I'm sure the notion would horrify some folks, but we've taken several trips and never gone near the parks. We've looked at these as lovely resorts, where we know what to expect, we can relax, have access to good food, sunny climate, reliable transportation, make ourselves at home and get a truly comfortable vacation. We both travel a fair amount for business, so often we are not looking for new experiences, we are looking to relax. DVC fills the bill for us.