We went to WDW in December last year and while the crowds are nothing like you find during the Summer months there will be lines on some days in the 35-60 minute range, starting around late morning on the E, D, C ticket rides (like Buzz, Dumbo, etc). It is still better than Summer wait times ranging from 45-120 minutes.
During some times of the day you can find some rides you can just walk right on. At night we typically found we could walk right onto IASW or the carousel without any wait, but none of the other Fantasyland rides.
So, we found it to our advantage to visit a park during the "New" Magical Hour (derivative of old EE) even in December...you can start your day an hour earlier by using this resort benefit. It is a good time to hit rides like Dumbo, Peter Pan, etc which typically have long and slow moving lines.
The hard part comes in knowing when to move toward the entrance in preparation to jump to another park before it really gets crowded.