Yeah, I know, it's not an answer, but it's really too long for a comment ...
Basically, conduit makes it faster to run cables later, but depending on what exactly you're doing, it might not be that fast -- if you don't know where you're going to need the cables to go to, and you don't have the necessary junction boxes to be able to re-route everything, it's not really going to solve anything.
Most of the problems with running cables are when you have to run them through, rather than parellel to wall studs, or trying to run cables in walls packed with insulation.
Because of the insulation issues, I'd be inclined to run conduit in those walls if the walls are open already, to the existing wall boxes, with the assumption that I could always either add a few more items to a given plate. (I tend to use quad leviton blanks, but could swap 'em out for the 6-hole ones, to give me a couple more items to fit in there).
But I wouldn't run them horizontally -- I'd run them vertically to either the attic or basement (if you're lucky enough to be in an area with basements), and bring them to where I could then run them through a larger chase. For interior walls, I'd just be concerned with knowing where the walls are in the attic, basement, crawl space, etc., so I could get into the wall cavity to add more cables down the road. (see my comment re: running wiring through a crawl space)
The only time you really have problems are on houses on slab that are 3+ story houses (can only really handle the top and bottom floors easily), or 2 story houses on a slab (can't run the lower floor to the basement when there's no basement). In those cases, it might be worth running conduit to a central location (eg, the attic), so you can then connect any two points in the house, even if it's a more circuitous route. But, as @shirlock homes pointed out -- these sorts of runs require capping or similar due to fire codes.
The only other times I can think that I might run conduit is if I were to have a wall that I couldn't patch easily down the road (maybe real wood paneling, or tile walls?), or if I had to run an outlet to somewhere in the ceiling, as it's harder to snake cables through the ceiling than it is the wall.