One problem with camshafts is that the
profile of the cam, that is, the complete set of valve timings which it produces, is fixed relative. In other words, whether the engine is revving fast or slow, the timings that separate the valve actions remain the same. The problem here is that the cam's designed profile is only maximally efficient within a narrow speed range.
One solution to this is called VTEC, or Valve Timing Electronically Controlled. In a VTEC engine, the timings between valve actions can be modified by the engine computer. The most common method of achieving this is to have a camshaft with various sets of lobes on it which the engine can displace laterally so as to choose which lobe set to use. If you have a DOHC engine, you can tweak the exhaust and intake timings separately, allowing a better match with a profile of optimum efficiency across angine speeds. VTEC is a Honda technology, and as far as I can tell involves shifting the cam profiles electromechanically between a high-rpm and low-rpm profile.
An even cooler method is lurking over the horizon. It is possible to do away with the camshaft entirely, and to move the valves by hooking them up to electromagnetic actuators. Then, you can trigger the valves individually simply by feeding power to the electromagnet; if you want, you can even modify the opening and closing time of the valve. Since this is done by controlling electric power rather than physical motion, it is quite easy to have the valves actuated by a computer, and simply change parameters in the computer's program to change the engine's tuning. In addition, it drastically reduces the number of rubbing moving parts, which increases engine reliability and means that the engine is less likely to suffer a catastrophic failure.
The nice side effect, of course, is that eventually you'll be able to tune your car, live, with your PalmPilot.