It's marketed as a recovery drink because it has carbs _and_ protein, in whatever the perfect ratio is supposed to be, 4:1 or something. An "energy" drink has carbs only, or used to, anyway, now it seems others are getting on the protein bandwagon.
I myself drink it starting midway through a long ride, and at the end. I like to drink it at the end of a run, or throughout the run if it is long- like ten hours.
I _really_ like the lime flavor (haven't tried the new choc or vanilla). I'd drink it way more frequently, probably replacing Gatorade with it, if it wasn't so expensive. Luckily, I discovered choc milk, which has virtually the same ratio of carbs/protein, plus a bit of caffeine and possibly fat.
The cheap way to buy Endurox is look on Froogle. You _should_ be able to find it for $1/serving, or close to. The place with the most consistantly low price I've been able to find is http://www.nutritiongeeks.com
Be careful when you mix it- I put a little water in my bottle, the two scoops of Endurox, then shake gently. Then add the rest of the water, but not completely up to the top, because it tends to foam. If I'm doing a run and leaving it in the car, unrefrigerate, I do the little bit of water/two scoops thing, fill the bottle with ice, then add water around it.
Yum!!