In computer science, what does winning a Sloan research fellowship say about an advisor?
The Sloan research fellowships are distinguished awards for early career faculty.  This means that your prospective advisor is considered a very talented young researcher.  However, it also means that your prospective advisor is not very far along in their career.  There are some cons to working with a young assistant professor as an advisor, including the risk that your advisor might leave the institution or not get tenure (not terribly likely for someone talented enough to get a Sloan fellowship but more of a risk in the generic case of working with a new tenure track faculty member.)  I think that most people would recommend picking a more experienced and well known advisor.