What I Say Now:
Okay, so I have relied on these as a substitute for gel for this past training season (on runs more than 15 miles). I simply get very hungry and need some sustenance after running for more than two hours, and hydration can only get you so far.
I have grown to love the Strawberry and CranRazz flavors of these bloks. They also come in Margarita, Orange, and a few others that I haven't tried. Like gels, you definitely need water to wash them down, though.
What I Said Then (10/16/06):
I had a sample of this lying around for probably longer than acceptable and ate it about an hour before a long run. I don't know if it did anything, but I think I received a nice spurt of early energy. They have a strange texture sort of like a huge gummy bear but are otherwise good eaten over an extended period of time with lots of water. I personally would not eat them while running, at least not before lots of practice.