I was showing all the new features of Illustrator CS4 to a group of designers this week, and someone in the class asked if there were a way to retract one of the bezier handles associated with an anchor point without disturbing or changing the angle of the other handle on the point.
I don't know of any way to easily do this in Illustrator. But while looking for something else this evening, I stumbled across BetterHandles from NineBlock Software. This nifty Illustrator Plug-in for Macintosh or Windows versions of Illustrator does exactly what the client was asking for, and much more.
Download the demo and try it out...it's really slick!