Microsoft Academic Search is a nice tool. It’s a shame it is built on Silverlight.
I’ve found the tool to be very helpful when you find an older academic paper on a subject related to something you are researching and you want to find the state of the art.
For example, I am taking a quick look at mining software repositories. I came across a 2005 paper on using Code Churn to predict defects from Microsoft Research. I looked it up in Academic Search and moved forward to find Studying the Impact of Social Structures on Software Quality, which is even more interesting to me. That paper led me to discover the conference on Mining Software Repositories (co-located with ICSE), which seems to have a lot of very interesting papers. Starting from the top of the best paper list, I found The Impact of Code Review Coverage and Code Review Participation on Software Quality, which is a well-written paper both presents relevant research and gives context to the latest-and-greatest references related to the subject. While similar results can be acheived by strictly working through references at the ends of papers, using the Citation Graph in Microsoft Academic search speeds up the process.