My wife and I have been on a low carb diet for the last 5 plus months and have both lost around 30 pounds. We do not expect to give it up any time soon.
I've been on a "normal" carb diet since April 1, 2003 - that's nearly 16 months now - and I have no intention of giving it up. I've gone from 304 to just under 200 pounds and I feel 20 years younger. I walk at least 5 miles every single day. Never had the energy before when I was loading up on carbs.
When I say "normal" carb, I mean about 100g a day. Not the 400g+ that you would eat by following that food pyramid.
A high carb diet was definitely the problem for me. It drained me of energy, made me tired and kept me hungry all the time.