I brewed NB's Bourbon Barrel Porter over the summer and tapped it about a month ago. It used 2 oz of medium-plus toast cubes and after doing a ton of research on it, I ended up soaking the cubes in a cheaper bourbon for a month and then dumping that bourbon (it smelled awful) and adding fresh makers and letting it soak for another 6 weeks. When I kegged the batch I poured the bourbon and cubes into the keg. The cubes stayed in for about 6 weeks and then the keg sat for a month or 2. I'd say the oak flavor is medium-strong, but not even close to overpowering. It was a nice warm vanilla note to it.
From my research, if you want a simple, quick, less complex oak note, use chips for 1-3 weeks. If you want a more complex, "deeper" oak note, with the vanilla, etc, use cubes for 1-12 months.
Chips have much more surface area, and an even char, and thus, they give off their flavor much quicker. The even char is the reason they are less complex. Cubes have varying char and much less surface area, but more wood overall, leading to the ability to leave them in longer. My takeaway was for a big stout or something similar that you are going to age, use a smaller amount of cubes for a longer amount of time.
Chips are good for IPAs that aren't going to age, but you want to impart an oak note quickly. I've never used chips, but I'd say 1-2 oz of medium to medium-plus toast for a week. Taste and then decide whether to do another week. If you don't want to add vodka or bourbon, you can also boil the chips. That will strip some of the oakyness from them also, which may or may not be a good thing.
