OAKING

Oak is gaining more and more traction as an avenue to great beer. Plenty of breweries are using oak to age their imperial beers, and the result are typically great. Unfortunately, whiskey casks are not a feasible option for homebrewers,  but there are a few ways to impart the same oak flavors in to your next batch of brew. 

Five factors influence how oak aging will affect your beer.
     - Form (chips, cubes, spirals, staves, etc)
     - Type (American, French, Hungarian)
     - Toast (light, medium, heavy)
     - Amount 
     - Time

These factors give you a lot to think about, but also open a lot of doors. The key is to understand how oaking works, and how each factor plays in to the final product.

BASICS
Its important to know that surface area is what drives the oak extraction process. More surface area yields more intense flavors more quickly, but that isn't to say faster is better. I for one, would argue that slow and steady wins this race, as oak flavors should never be the main component of any beer. Also, if you think of how commercial brewers perform their oak-aged beers, the amount of beer-to-oak contact is relatively low. An average whiskey barrel has internal dimensions of 35" tall and 21" wide. That means each barrel can hold 54 gallons of liquid and has 2310 sq in of surface area. To scale that down to a 5 gallon batch, one would need about 43sqin. per gallon (or 215 per 5 gal) which is about the area of 1/2 a sheet of paper. 

FORM
Oak comes in several forms, each with its own process. Mainly chips, cubes, and spirals.

Chips are basically wood shavings. They are not uniform in shape, but they are always small and thin. Therefore, they have a large surface area to weight ratio and extract rapidly. Most homebrewers speak poorly of chips, and I would avoid them. They are unwieldy and make transfer more difficult.

Cubes are commonly the the size of dice (.50in -.75in), but can vary. They have a uniform size and are typically recommended by homebrewers. They are usually thicker than other oaking options and thus have a lower surface area to weight ratio. This means they extract the slowest and are the easiest to control.

Spirals are exactly what they sound like. The are long spirals with more thickness than chips but less so than cubes. I haven't heard many opinions regarding them, but would imagine they are fairly similar to cubes. Soaking spirals would be difficult though.

Oak Essence or powder, provide more of a one-off change. Aging is not required, but the flavors are not nearly as complex. This is more of an oak-imitation process in my opinion. Not to say it shouldn't be done, but its not my cup of tea.

Oak also comes in honeycomb shapes, stave (slices of old barrels), and many others. With the information above, you can probably deduce the pros/cons of any type.

TYPE
There are three common types of oak; American, French, and Hungarian. 
     American oak is most common in the beer world, as it is used to age whiskey. Its lends an mild sweetness, vanilla notes, and full mouthfeel. The go-to oak if soaking with spirits.
     French oak is more mellow than american oak, but provides more rounded mouthfeel.  Its also known to impart more spicy (confectionary) notes, reminiscent of cinnamon. 
     Hungarian oak is the vanilla king, with some bittersweet chocolate and coffee flavors at the heavier roasts.

TOAST
The more toasted the oak is the more prevalent the difference between varieties. Light toasts provide woody and coconut-like flavors and more mouthfeel, while heavy toasts lend themselves more to flavor. In most cases, you should match the toast to your beer. Light beers perform better with lighter toasts, whereas heavy beers can stomache heavier toasts. Unless the beer is very light, I would recommend medium or medium-plus toasts.

AMOUNT / TIME
The amount of oak used, and the length during which it is used sort of go hand in hand. The oak flavors change as the aging process continues, so it is best to sample as you go. At minimum you should take a sample every week and reevaluate your beer. There isn't anything worse than over-oaking and dumping a batch. Most brewers recommend using 2-3oz of cubes per 5 gal for 3-4 weeks. I would definitely recommend those guidelines until you can gather more experience and adjust as necessary. I would generally prefer the oak to be hardly perceptible than too strong. 

PROCESSES
There are a few ways to get oak flavor into your beer, that don't include actually putting wood into your beer. You can soak the oak in warm to hot water and make an oak tea. Then you can add the oak tea to your fermentor and there is no need to worry about the sanitation risks associated with oak aging. Additionally, you can soak your chips in liquor (liquor tea) and then add the liquor instead of the oak. This is illegal in the case of commercial brewers to add liquor to their product directly (hence the whole barrel aging thing), but since you are a homebrewer there is no need to worry. I have added liquor to my secondary before, and the batch turned out fine.

CREATIVITY
The bourbon aging beer trend has come to a fabulous place, where barrels change hands over and over again, each time creating a new dreamlike substance. Many people have consumed some time of oak aged product, be it bourbon or beer, but it doesn't have to stop there. 

New Holland brewery ages their Dragon's Milk stout in old bourbon barrels, then sends those barrels over to their distillery to age their bourbon, creating beer barrel bourbon. An even crazier relationship exists between two Grand Rapids partners, Founders and BLiS. Kentucky whiskey casks are sent to BLiS where they are used to age maple syrup. BliS then sends these same barrels to Founders so they can age their Kentucky Breakfast Stout. Founders then returns the barrels to BLiS so they can age their hot pepper sauce. Crazy, right?

While this style of second-, third-, and even fourth-hand use may not be applicable to homebrewers, it does prove that amazing things can come from oak aging. You might want to try a simple approach during your first few goes around, but don't limit yourself. Get creative and try some weird stuff. 

MORE INFO
I have done a lot of research, but do not have a lot of experience with oak aging. Luckily, the internet is swimming with practiced homebrewers who are here to help. If you want some more information on oak-aging, check out any of the articles below for more information.
     Beersmith - Oak in Your Beer (Oak Chips & Barrel Aging)
    Great Fermentations - Oak, Bourbon, & Homebrewing
     The Mad Fermentationist - Treatise on Oaking Homebrew
     More Beer - Using Oak in Beer