[mattangriffel]

The real reason for getting a fixed gear bike is that there are less parts to maintain. They don't have all those gears so they can be much lighter. They also tend to not break as often. The downside is that you don't get the advantage of being able to switch gears, which tends to not matter in cities like Manhattan because there aren't many hills and you never reach high speeds for long stretches anyway.

On top of that there's an aesthetic aspect to the simplicity. I tend to find them really beautiful in a post-modern art kind of way.

[fennecfoxen]

That's the practical reason. The real reason, though, is street cred. ;)