Though initially attributed to an innate perception bias, apparently, it's very likely that cars in the next lane actually moves faster, ala thermodynamics:

Adopting a thermodynamics perspective, it is easy to see that (at least in the ideal case) increasing the "diffusion rate" (that is, the probability of lane-switching) will speed the approach to "equilibrium" (where there are equal velocities in both lanes), thereby increasing the road's throughput and the number of vehicles that reach their destinations per unit time.

Which means constant lane-switching is good for the speed.. we probably already do this to some extend.. of course, the true "value" of a lane should probably take account the safety factor and the switching cost isn't always free, but if you only value speed, darting across lanes like a maniac is the way to go!