Came across this great time waster...
GeoGuessr - Let's explore the world!
It dumps you somewhere on Google streetview, and you have to guess where you are (no cheating with google open in another window!).
One of the fun features is that you can create challenges for others, where they are presented the same locations, and compare scores:
TheMentat's Throwdown
My score...
11,912:
TheMentat's Score