I only see it clockwise, too lazy to damage my eyes to see the other version.
Personally I like the more instant effect type, stuff like after image is too tiring.
Stuff like simple 3D effect, real-life impossible objects and color/size/etc variety.
If you guys like optical ilusions you can get them by the ton at
http://www.moillusions.com/
Edit -- Heh.. I accidently saw it right after writing this.. the trick is to not look at her legs.