Certainly homebrewers are not new to the idea of adding oak or liquor to our beers. For years homebrewers have been adding clean oak to our fermentors (just as some craft brewers were/still do) and bottles of whiskey have found their ways into our beers. However, the barrel is treated as something very different, where the oxygenation through the wood has an effect along with the oak character and whatever is coming in from the alcoholic beverage that once filled the barrel. I'm suspicious that barrel aging is really that beneficial to homebrewing.
For commercial brewers there is no question that barrels provide a unique service to the industry. Commercial brewers seeking to add that bourbon barrel aged effect has no choice but to literally use a bourbon barrel because the law explicitly prohibits fortifying beer with liquor or any other alcoholic beverage other than more beer. Homebrewers can get away with dumping a fifth of Makers into the fermentor (although actually most/all states probably prohibit this, too) without having the state alcoholic beverage commission come lock up our mash tuns. Barrels are also relatively cheap storage vessels. Those large 55-60 gallon barrels can be found on contract for around $100-150 so it's not cost prohibitive. Vintners sell old barrels to keep their wine in fresh oak barrels. Bourbon distillers, by law, must age bourbon for at least three years in fresh oak barrels so there are always bourbon barrels needing a home. Other liquors also use these barrels on their own but will also look for ways to recover some cash while disposing the spent barrels. Brewers can find uses for all of these (for example, Austin-area Twisted X uses tequila barrels to age its imperial schwarzbier and Jester King is aging sour beer in mezcal barrels).
Homebrewers, on the other hand, seem to be paying out a lot of cash to grab barrels. Five and ten gallon barrels are especially sought after by homebrewers because the size matches our normal brewing amounts. There are some wine and liquor barrels floating around at this size but they seem to sell for close to the price of those much larger barrels. Dropping $100 on a really awesome looking fermentor wouldn't be that big of a deal if it didn't have a strong probability of a limited use period. Whatever liquor or wine was aged in the barrel will eventually get stripped out of the barrel, leaving a fairly neutral barrel. While most homebrewers seem to think once that happens they will convert the barrel into a sour-aging barrel, there is a strong likelihood that the barrel will get infected -- in a bad way -- before that happens. With the oxygen permeability of the smaller barrels, the likelihood of an acetobacter infection is much greater. Overall, many homebrewers seem to not have a good understanding of barrel care which means the probability of an acetobacter or other infection is quite high. Some brewers are coating their barrels in wax or lacquer to reduce oxygen permeability but improper sanitation during/between filling won't be helped by the coating. Sometimes barrels just turn on you and produce some terrible beer. I strongly suspect we will see a flurry of acetic and other faulted barrel-aged beers coming into homebrew competitions over the next few years.
Still, barrels might be worth the cost and worth the risk if they can produce something you can't replicate in other forms. After all, if you can soak some oak cubes in bourbon and toss it all in the fermentor and get the same flavor it hardly makes sense to spend $100 on something that may produce infected beers except it will look really cool sitting in your house. Some people suggest the flavor from the barrel is richer and more complex than adding liquor-soaked oak cubes. The idea is that when the barrel held its original occupant, the non-alcohol part of the liquid soaked into the wood, leaving a delicious syrup trapped in the oak. When beer is added to the barrel, this syrup flows back into the beer. I assume that concentration in the wood takes more than the week or two most homebrewers rely on to soak their oak cubes so the barrel is definitely gaining a benefit over the old cubes.
I wonder whether aging the cubes in liquor or wine for months/years would produce the same flavor results without the work involved in cleaning barrels and the risk of infection. If so, then homebrewers could produce beers with the same quality barrel aged flavor with all sorts of liquors and wines by keeping a few mason jars of oak cubes sitting around. There's good reason to believe the thickness of the oak staves has something to do with the quality of the oak character and the amount of syrup that can be produced within the wood. That could also be emulated by using larger chunks of oak rather than cubes. I do have some jars myself with liquor and wine with some old oak chips I bought but never used. I plan on letting these age for a few months before using them so I guess in a few months I'll know whether that hypothesis is true. Of course, it could just be the case that the imperfection of barrel aging adds an attribute to the beer and makes each one unique in a way a mason jar full of wood and whiskey just cannot deliver.
I can't say I haven't thought about buying a barrel...many times. Given my thoughts above, I have a hard time justifying spending the cash on a barrel even though the idea of looking at a barrel in my house and feeling connected to the historical sense of aging beers in wooden casks is very appealing. As appealing as it is, it losing some of its luster when I think about pulling out abeer and having to dump it because it has a nasty infection.