Why do I do the "saddle shuffle" when riding?
It all depends on your saddle. As someone who has just been enlightened, some saddles are supposed to be pointed a bit nose up. Take the brooks flyer for instance, it is not the front that is supposed to be level. It is the back making the front point a bit upwards. I think of it less of a seat then a hammock. 

I have also had a saddle that was a left over from my fat days that provided extra back support. Because of it's design for bigger behinds, and me lacking one for the first time in a long time, I kept sliding forward which was hurting my taint (for lack of a better word).

Try angling your seat up a bit or maybe moving it forward a bit on the rails. Play around with the fit and see what kind of results you get. If all else fails you can go to your LBS and ask them to take a look at it for you.