According to Mike Burrows, legendary bicycle designer, bicycles should come standard with 150 mm cranks, and he uses 140 mm personally.

http://www.bhpc.org.uk/short-and-sweet-a-discussion-on-crank-length-by-mike-burrows.aspx

For me changing to short cranks changed cycling for me. It made much longer trips possible because greatly reduced stress on the knees.