Same thing, sort of:
http://www.cbc.ca/consumer/story/2009/08/04/hybrid-study.html"Our estimates indicate that two-thirds of people who buy hybrids were going to buy them anyway," said Chandra. "So for the majority, rebates are not changing behaviour — they are subsidizing planned purchases."
I believe the same can be said for cash for clunkers. If you take advantage of it, you were probably planning to get one anyway.