i don't know of any organized rides, but the roads can get crowded and narrow. i've always found it best to ride EARLY in the morning....

stay clear of the bicycle paths....they are crowded with children and walkers. i was hit pretty badly two years ago by a guy on a $7000 carbon bike who couldn't unclip and lost control of his bike, hitting two walkers and me ($1000 damage to my bike). have fun, though...it's a beautiful island to ride