Now I've only been to one gym but the bars for the Smith machine there are only 15 lbs, no way are they close to 30-40lbs. And it's possible that you've just gotten to a point where you aren't progressing like you used to, you can't keep going up 5 lbs every two weeks for forever. You need to switch something up in your routine to shock your musclesso that they don't get accustom to doing the same amount of weight every time.
And regarding the smith squat questions, I found <a href="http://www.exrx.net/ExInfo/SmithSquat1.html"> this article </a>to be pretty informative.