I discovered energy gels a few years ago and decided to try the Powerbar brand on an AT hike in 2004. If you've never tried a carbohydrate gel or don't typically take in caffeine all I can say is WOW! I had put in a long day and still had 3 miles to go when I hit the wall. I took in a double caffinated dose of Powerbar Gel and 20 minutes later it really kicked in. By the time I reached my destination I felt like I could cover another 5 miles!
I have tried various other brands since then, and keep coming back to Powerbar. I like the taste, especially the Tangerine and the Strawberry-Banana. I also have since learned to gauge my caffiene needs to the trip I'm taking (none, single, or double shot). They definitely give me the extra punch I need when I need it.