Affordable Web-Scale Computing
With the launch of Amazon S3 (Simple Storage Service) we are seeing a continuation of the trend for the big web companies to monetize their computing infrastructure by opening it up to developers.
It is probably only a matter of time before we see Google create something similar, which would essentially be a limited public interface onto the Google File System.
I would love an API that exposes Google's MapReduce, a simple programming model for crunching on large datasets. You can write and run MapReduce programs today, using Hadoop, but it's only really useful if you have enough machines at your disposal. The pay-as-you-go model of S3 (and Sun Grid) would be very attractive to developers who want to run ad hoc computations, or can't afford the upfront investment in hardware.