Not a cable replacement
I really don't see Netflix as any kind of alternative to cable/satellite subscriptions, except for those that are seriously considering cutting the cord (or already have). From what I could tell, the current selection of TV shows available in the US is both limited in variety and age (I didn't see anything that wasn't available on DVD already), and if previous patterns hold true the selection in Canada will be more limited. Unless all you watch is movies or heavily syndicated reruns, Netflix will be a suppliment and not a replacement.
However, I do expect it to take a chunk out of the subscriber numbers for the premium movie packages and pay-per-view sales. It may also succeed in getting some people who have cut the cord to pay for some content again.