We’ve now passed an inflection point. The race used to be about increasing the number of megapixels, and to some extent this is still seen in the idiotic megapixel increases in the consumer digicam market, where merely zooming the lens can approach or even exceed the ability of the lens to supply adequate resolution to the sensor (smaller aperture = diffraction).
The new race becomes one in which usability and overall image quality become the market differentiators. This includes things like self-cleaning sensors, lighter weight, longer battery life, WI-FI, frame-rate, buffer size, color accuracy, dynamic range, high ISO performance and improved optics.
There will be continued incremental increases in megapixel count; expect Canon to introduce a EOS 1Ds Mark III at 22 megapixels or so, a realistic optical limit with a full-frame sensor. Such increases are likely to stop at around 28 megapixels for full-frame sensors, unless optics improve dramatically. Nikon already has nowhere to go with its smallish DX sensor; the photosites of the D2X are already so tiny that low micro contrast is an issue, even if the optics can supply adequate resolution—and critically-accurate focus is a very real problem.