Originally Posted by slantrock
Even though I didn't notice any symptoms from the wobble, there must have been some cost, however minor, in terms of pedal power and efficiency, since the chain was not running through the cogs as smoothly as it does when there is no wobble.
Actually, it will be a bit in both directions: good and bad. For half the rotation, the cog will be approaching an improved chainline, and for half, it will be approaching a worse chainline -- unless the cog would normally offer a perfect chainline, but there's only one of those per chainring -- the other 9 cogs (or 8 or 7...) are out of the chainline.
Either way, it's really minor, and really common. Your Mavics will probably exhibit this behavior at some point too as the freehub bearings wear and deform.