Most of the examples people would come up with of extremely compute-intensive tasks are parallel algorithms, and those would be cheaper to run in the real-world on server farms which do not need self-contained powersources fitting in an HTC or similar special setups or attendants paid handsomely to be willing to spend a year isolated in the prison of HTC. There's simply no reason to take a highly parallel task and run it in an HTC when you can get the same result at less cost and less latency by running it on a perfectly normal server farm or cloud computing platform.

(The genetic algorithm will spit out similar answers if you run it on 1 CPU in a HTC at >$1/day for >$365 or if you run it on 365 CPUs on Amazon EC2 at $1/day for 1 day total for $365.)

Remember, electricity is already the dominant cost to running a server these days!

Are there serial tasks which people do not run because they would take a fraction of a year but if they could be run overnight would justify a years' worth of premium power bills? I'm sure there's some and the introduction of an HTC would conjure up some uses which no one had bothered to work out because it was obviously pointless, but I can't help but think that there being no obvious candidates means the candidates wouldn't be fantastically useful.