Deadlifts - Smith machine or dumbbells? (no barbell)

Tip: I wouldn't squat with the smith machine for the purpose of safety.

Here's a couple of links that go into detail why this tip is a good one.

http://www.menshealth.com/mhlists/avoid_lifting_injuries/The_Smith_Machine.php
http://getfitguy.quickanddirtytips.com/top-7-exercises-to-avoid.aspx (tip #7)

There are probably some decent exercises that one can use on the smith machine, for what it's worth, I use the smith machine for standing calf raises.