The short answer: yes.
I pulled over a lb of Maui from a cheapo hydro store 5 gal black bucket last fall. I don't know how much over, maybe a couple ounces...anything over ~460g went directly into a big bag for me and my friends to smoke
Also I helped with a friends guerilla last summer in which they used all 5 gallon buckets spray painted like camo. We drilled like 1/4" holes in the bottom of each pot..maybe 8-12 holes in each one and the roots were growing from the bottom into the ground. They were not pulling a pound each, but im sure some of them were pounders.
If you wanna see pics of huge yields from 5 gal buckets, check out fdd's outdoor '08 thread. He had a plant in a 5 gallon bucket that must've been a 2 pounder. The fucking plant would fall down from its own weight if there was a slight dew in the morning. I don't think there was actually any soil left in the bucket by harvest...just 5 gallons of pure white roots lol. Not sure if it was Santa Berry, or maybe GDP... Or was it the HiJack?
Anyway, it IS possible but sodalite is right... its like a million times easier to grow a 1 lb plant in a 10 or 15 gallon bucket than it is a 5 gal.