The AMC White Mountain Guide suggests that "Descent by this route is not recommended". This warning is mostly aimed at casual hikers, not seasoned climbers, but it is a fair warning none-the-less. The rocks become quite slippery in rain or fog and it's a pretty exposed route.
Of course, when my college roommate and I descended this route back in 1994, we were young and stupid and, more importantly, hadn't read the relevant passages in the guidebook. We arrived safely at the bottom of the ravine and met a group of climbers roping up for an ascent. They looked fairly surprised to see us come sauntering down in tennis shoes.
Your milage may vary...
Good point...I should've mentioned that.
I think mostly, this warning refers to the scenario when a party decides to use the trail as an escape route out of a storm up on the Garden. In this scenario, the rocks are garaunteed to be slippery.
I've never gone down it - not so much because of this warning, but because it makes for a nicer, more interesting loop to go either over Tucks, Lions Head or Boot Spur for the descent.