For Olympic Lifting, the order usually goes Front/Back/Over-head squat(as mentioned, you squat with the bar held at lock-out, the Chinese squad use it a lot now). Also, if you look at the 2 major lifts(three if you count the discontinued Clean and Press), there is a decent amount of front squatting during the first part of those lifts.
As an aside, the general rule was that a good lifter should be able to Clean what they can Front squat for a triple. The second part of the lift, the Jerk is usually a tiny bit under what you Clean.
Front Squat usually equals 85-90% of back squat.
Snatch equals 80% of C/J or 60 to 65% of back squat.
I have not seen or can remember ratios for OH squat. But I guess 3/4 of your best back squat is a good number.
