We've all wondered why top aligned labels perform better. This article explains and illustrates why. What has your experience been?
Read the article: Why Users Fill Out Forms Faster With Top Aligned Labels
Don't forget about LukeW Web Application Form Design !
More Detailed Analysis
Rapid processing since label and field are very close...From Luke's photostream http://www.flickr.com/photos/rosenfeldmedia/2366428797/sizes/o/in/photostream/