I don't think I understand how the size of the container makes a difference in the amount of priming sugar.
I've not bothered to figure out the physics of it, but I know it to be a fact. Perhaps it has something to do with the ratio of head space in the container to volume? Anyway, less is better in this case.
I've got a couple of those mini-kegs lying around and hate to see them go to waste... This is a perfect way to keep that from happening. Cheers!
Re-using them is pretty simple. You can use them as casks, like Lennie is doing, put them in one of those Beertender deals (like Dave), or buy/build a tap for them and just use them like corny kegs. You can also rig up a schrader valve on a barbed fitting and force carbonate in them. I must have six or more filled and waiting to be tapped, along with the rest of my kegs and bottles.
One thing I've found on cleaning them is that it's hard to get them dry. They don't drain fully due to their shape. I push a clean rag or paper towel partially into the hole and shake until it absorbs all the loose water, and then let them air dry.
There's a good thread on NB forums on building a tap, if you're interested. I've built three recently, but haven't had the opportunity to pressure test them all. I know one had a leak, unfortunately...