Sorry to keep cluttering up this thread, but I kegged my first beer off of the barrel, and I wanted to share my experiences. I figure more people are looking here than anywhere else.
I brewed a very cliche imperial stout to put into the barrel, after having tried a lot of wonderful, very sweet, foreign imperial stouts. OG of 1.097, FG came down to 1.023 with WLP007. Roasty, Chocolatey, smooth, and boozy when fresh. (Amazingly I got it to ferment out and clear in about 10 days.
Took the liquor barrel, which still had some residual booze i've been using to keep it swelled. Put a few gallons of water in and then dumped to clear the booze and sediment (if there was any). Beer goes in.
After 7 days, I pulled a sample to try and was surprised to find the liquor flavors were starting to overpower the beer, even as big as it was. By day 10, they were definitely overpowering, so I kegged the beer from the barrel, added a liter and a half of booze back into the barrel to keep it swelled and sterilized, and I'm going to let the stout sit for a while.
Moral of the story: those of you who are planning on months with lesser beers- taste your beer before letting it sit too long.
Although I suspect the more I use the barrel, the longer it'll take and the more oak flavors will come out instead of the liquor flavors.