Apple shipped Leopard in October, 2007.
So Vista's been out 6 months longer than Leopard.
Stats for f.lux users:
88% of mac f.lux users are using Leopard
27% of windows f.lux users are using Vista. (Most of the remainder are on XP.)
For a paid upgrade to convert at that rate is amazing. Apple is just kicking butt.
[This is just data from Google Analytics. f.lux isn't phoning home with any of the above.]