Re: Holodecks aren't just about processing power
Tactile sensation is already here in primitive, solid-mass form:
http://www.novint.com/index.php/games/whatis3dtouch
Also, the ability to move forever without going anywhere, in any direction, without smacking into the walls is in prototype:
http://spectrum.ieee.org/automaton/robotics/robotics-software/cyberwalk-giant-omnidirectional-treadmill-to-explore-virtual-worlds
And the ability to look behind objects based on your view point has been worked out using a Nintendo Wii:
http://hackaday.com/2007/12/21/wiimote-head-tracking-desktop-vr-display/
Olfactory...well, we can't have everything now, can we, or else we'd have build the thing! Though there are companies working hard on that:
http://www.scentcom.co.il/
So here's what we still need:
-Artificial olfactory creators
-The ability to "solidify" energy (true force fields) and change those fields into whatever shape we want, while allowing un-protected manipulation during the simulation (it's not a real holodek if you HAVE to wear gloves when you go in)
-The ability to track ones head position without having to wear anything or being able to see the cameras (should be easy if the force fields are made, just hide cameras behind them)
-Seamless, near omni-directional screens which would allow a seamless picture to be presented.
-Advance all technologies out of prototype and integrate them
Bonus points if the ability to seamlessly and instantly turn on/off sensory deceivers depending on the user's current viewpoint (i.e. If they can't see it, why waste resources showing it). This would actually go BEYOND the Star Trek holodeck's capabilities by providing massive energy savings and allow resources to be concentrated where they're needed most at current, rather then wasting them on effects that mean nothing (Zelda Ocarnia of Time made use of this trick).