Here's a humorous Peg short from Superman #136 on a leap year tradition:
This sequence from Lois Lane #19 might be a little surprising:
In the story, Lois has been hypnotized into forgetting about her affections for Superman and decides that maybe her co-worker deserves a shot, alarming the heck out of Clark.
Update: In Green Lantern #3 (Nov-Dec 1960) Green Lantern experienced the Leap Year Menace: