As you can see from the pic, the stock seems to have separated. It went right into the freezer, where it has been for three weeks. Took it out last night, and it thawed overnight, in the fridge. Is this normal? It smells fine....
Looks like a little fat at the top, that's normal. Some unfiltered suspension at the bottom. That's pretty normal for a home stock.
There's plenty of time in the freezer for separation before freezing. Indeed, freezing could actually cause some precipitation. Basically as water starts to freeze, it bonds preferentially with other water. Suspended solids can be forced out of suspension so the water can bond.
As phatch said, the stuff at top looks to be fat that has solidified. It can easily be removed. The "stuff" on bottom are exactly as he described-suspended solids forced out of suspension during the freezing and thawing process. These solids are "normal" and is why some stocks are cloudy. You can avoid cloudy stocks (lots of solids in suspension) a number of ways although I feel the best way is to not cook your stock too hard. I bring my stock just up to a slow boil, reduce the heat immediately and allow it to simmer, never letting it boil again.
You could also clarify your stock to help this situation, using any number of methods, if you really desire crystal clear stock, but for most uses the slight cloudiness really doesn't present a problem.