I usually blip the throttle when down shifting......never gave it much thought.....just feels right. In this month's C&D (Cayman article) there is an explanation why it makes sense...

" It helps adapt the engine's momentum to the lower gear, preventing the destabilizing effects of drag torque."

The description was mainly in reference to driving in slippery conditions. Some might refer to it as rev-matching I suppose. Seems most appropriate when you're not just coming to a stop.....but with the intentions of speeding right back up.

With this stick (sort of related) to get a smooth acceleration you have to keep the revs up when up shifting also.