Deep wheels are for going fast. If that's what you care about then get some. But they're also expensive. Also IME I haven't noticed a difference for anything under 40 mm (including deep V's), then it has started making a difference (for me). The purpose of the depth is to reduce spoke area b/c wind gets caught up and bounces around in there, so depth is #1 . After that width, U-shape and other things like [MENTION=418438]TimothyH[/MENTION] mentioned add up but it's mostly about reducing spoke area (depth).

Also if you care about going fast, tires and tubes actually make more of a difference then rim depth and they're cheaper.