Do Links Need Underlines?
http://www.uie.com/brainsparks/2006/07/05/do-links-need-underlines/

Spool, Jared M.
User Interface Engineering
2006

Abstract:

During our recent Virtual Seminar on home page design, several people asked about whether it makes a difference if links are underlined or not. It's a good question and one we get frequently.