One of the really cool innovations to come up back in the late 90's was the concept of a cluster computer-"Beowulf Cluster". Making a bunch of low cost, lightweight computers run as one unit. Envisioned by a couple of budget strapped NASA scientists, eventually supercomputers around the world were built using the technology.
"The Cloud" is the continuation of the concept. There are high availability, load balancing and high performance versions in use and the concept has also spread to hosting databases.
I have had several iterations of Lil' Rascal - named after Our Gang and the Little Rascal TV Show characters - and still want to build bigger and better versions of it. While the Pentium 4 was a rare turkey for Intel due to design flaws and pressure to keep releasing newer processors to keep up with the hype, when joined with other nodes it can provide the ability to crunch data at a reasonable cost for the budget minded. I got them all for free!
Moore's Law on the doubling of CPU power every year has held true until recently. And now, a current CPU with caches and dual cores, pre-processors, etc. have exceeded the power of multiple Pentium 4's put together. Still, its a great way to process lots of information in a fun way, plus learn the concepts of cluster computing.
I have crunched stats for fantasy football, stock prices, and lottery numbers. I haven't hit the jackpot yet, but at least I am having fun doing it.