Did you know that the most recent version of the MSN Search engine uses neural networks to improve search relevance? The ultimate goal is to have near-perfect relevance. The algorithms were developed in collaboration with Microsoft Research, with help from Chris Burges and others.
I used to program neural networks in college, but I haven't read anything about them in the last years. I believe that it's a fantastic research area, for example in speech recognition, or in OCR software. Neural networks shine especially in classification problems when there is a high level of incertitude (or noise) in the input data. However, I never thought to apply this thing to a search engine. (Hmm.. maybe I should pick up a modern course in neural networks and bring myself up to date).