Matt Hobbs penned a really good description of the role of a front-end developer.
A frontend developer bridges the gap between technology and design. They are a cross between an interaction designer and a software developer.
All frontend development work should be focused on putting user needs first. A frontend developer is the person that all the team's work flows through. They will ultimately collaborate with and communicate the work of a whole agile team to the user. (via @adactio)