I've been doing a lot of scalability research lately. The High Scalability website has been fairly valuable to this end. I've been thinking of alternate approaches to my application designs, mostly based on services. There was an interesting article about Amazon.com's architecture that describes a little bit on how they put services together.
I started thinking about an application that I work on and how it would work if every section of the application was talking to each other through a web service or sockets passing JSON or Protocol Buffers rather than the current monolithic design that uses object method calls. I then had the thought that why limit your services to being deployed on a set of static machines. There's only so much expandability in that, what if we harnessed all of the unused power of the client machines that visit the site.
This will work a lot better on CPU intensive processes than it will on memory intensive ones. For example, sorting a large data set requires some CPU, but a lot more memory because you need to keep each element in memory that you're sorting. Sending entire large lists to clients to sort and receiving the results would be slow due to bandwidth and latency restraints. However, performing large computations on a smaller series of data such as what's done with SETI or brute force cryptography circumvention where you can send heartbeats of partial results back, there could be a benefit.
People like games.