It's amazing what a facelift can do to the perception of a project. There are some really great projects that look abandoned or the docs are really difficult to use that prohibit me from giving them a fair shake.
This isn't as crazy as it might seem - using a modern home page design proves that someone has been investing time in the project since that design became popular.
Using the "trend-du-jour" for a homepage quickly communicates to viewers that the project is alive & active. It's a much more accessible signal than mailing list or commit history (although those are clearer, more accurate signals of project health).
