1. Many such applications want their computation to be highly responsive-- the long turn-around involved in farming your task over a WAN is often prohibitive. (E.g. real-time graphics.)
Use the right tool for the right job. Cycle sales are useless for most applications, and forcing a square peg into a round peg will only result in frustration. There are a gazillion useful outlets for this technology, though - more pop up all the time. The latest I heard today was OCR .tiff -> .txt conversion, where the payee can afford (cpu-wise) to toggle all the settings to the highest (slowest) quality.
2. Also many applications that need this kind of power are highly sensitive to inaccuracy or fraud. A scientific modelling experiment which uses zillions of cycles can be rendered completely worthless if a tiny calculation that had been farmed to Joe Blow is done wrong or is lied about by Joe.
Voting - send the same data to 3+ unrelated machines (if you can afford redundancy) and accept the 'majority opinion'. Sanity checking - depends on the algorithms in question; may require human intervention in many cases, where errors (accidental or not) may not be easily machine-recognizable. ... just to name a couple of the top of my head.
3. Similarly, many such applications are highly confidential.
This is the easy one :) That is to say, solutions to this problem are already being implemented for other applications. -- Jay Campbell edge@got.net - Operations Manager -=-=-=-=-=-=- Sense Networking, Santa Cruz Node Jay@Campbell.net got.net? PGP MIT KeyID 0xACAE1A89 "On the Information Superhighway, I'm the guy behind you in this morning's traffic jam leaning on his horn."