Finally got my 20# CO2 tank, and boy was I surprised at it's size.
Here's a shot of it with a standard DVD case in the shot for relative size comparison. However, it's relatively light (relative being the key word). I can easily carry it with one hand. Dunno how manageable it'll be when it's filled.
A word of caution for anyone looking to purchase one. It's more imposing than it's dimensions suggest, at least for me: 8" Diameter 27.5" Height. A good idea would be to see it in person before you buy it.