
I discovered Rocketdock by accident one day. Stumbling onto it I had no real idea what I had found, I downloaded it anyway and started to play. It seemed like a nice little add on for XP, however, I don't use the dock a whole lot in OSX and wasn't sure it would be very useful. As I delved deeper into Rocketdock I realized there is a whole world of user driven icons and add-on's which make it incredibly useful, to the point where it is now an integral part of the XP OS for me now.
Extensions such as stacks are fantastic, allowing you to view the contents of any folder in the dock as a grid or fan, much like in OSX, tip-o-the-hat to mantonga's for that one.
All in all I would say Rocketdock is a must for anyone wishing to have a more Mac like experience on a PC.