The books I've read state that the purpose of the zigzag arrangment is to slow the viewer down so that they will take more time to observe and experience the garden.

I've heard of no such superstition.

Dennda et al,

The superstition is based on an old Japanese belief that evil spirits can only travel in a straight line, hence a zig-zag bridge pattern to throw them off track...

Of course, many gardens in Japan use straight bridges as well (check out the pics in any book on Japan), so this old myth isn't taken too seriously. Either that, or the darn designers forgot to ward off evil spirits like they were supposed to, and anyone walking over, say, a straight stone bridge will be zapped by evil spirits. Hasn't happened to me yet, but ya never know...