I learned a couple years ago, and have taught several people how to since then. It does make some new connections somewhere in your brain...kind of crazy.
Study: Learning to Juggle Causes Changes in Brain
http://story.news.yahoo.com/news?tmp...ce_juggling_dc
Mastering the skill increases the amount of gray matter in areas of the brain that process and store visual information, proving what was not thought possible -- that new stimuli can alter the brain's structure.
A comparison of brain-imaging scans of non-jugglers and other volunteers before they learned to juggle and three months later, revealed an increase in gray matter in certain areas of the newly trained jugglers' brains.