Deans are great, if only for their versatility. They're good for applications up to 110 amps. Not many other connectors can boast amp ratings like that. And they're very light, too.

The only real reason I can think of not to use them is that they can be a bit annoying to unplug when they're brand new. Once they've had a few passes in and out they're OK, but they can be pretty stiff out of the package.

Certainly not a deal breaker, and alot of people have come up with interesting ways of overcoming this, including grinding indents into the plug for more grip, attaching hooks, covering the contacts with grapphite (pencil) to make them more slippery, etc.