There's been a lot of these kinds of projects. And they aren't always as popular as the project members think they will be.
Ubuntu is popular because of GNOME, which is a simple and beautiful GUI, and Ubuntu's apt front-end which makes it easy to install applications and run updates.
The Longhorn Linux team should have tried to mimic Windows 7. At least Windows 7 has Snap, and the Longhorn team could've written a Compiz plugin to introduce that feature in Linux.
But now, there's no real advantage of mimicking Vista in Linux.