I think you'll get the full credit since it's treated as a discount -- aFAIK the rental is still in the system as 4 days.
(That said, even if it isn't, the $ saved is far more valuable than the points you'd be forgoing if you only got credit for the 3 day rental.)
Originally Posted by yashan
How does the free day PC# affect the earning of points? If, for example, I get 50 points per day, would a four day rental only count as three and thus earn me 150 points instead of the full 200?