The simple answer is A LOT! Figure skating blades must be ground to create a hollow. The depth of the hollow depends on the skater's preference and the discipline they skate in (freeskate versus dance). The hollow creates two edges, inside and outside. The big rule of thumb is: NEVER EVER give your figure skates to someone who only sharpens hockey skates or use any automated skate sharpening machines which are found at some arenas. Trust your skates to someone who knows what they are doing. Close to Coquitlam, there are excellent skate sharpening services at the Skater's Edge Shop. Brad McLean is their master skate technician and this guy knows his stuff. If you want to know about the science and technical stuff about figure skating blade sharpening,check out this excellent website:

How Frequently Should I Sharpen My Skates? Once you feel that your edge is slipping, skidding or you lack the control you feel you normally have, it is time to sharpen. Some skaters don't mind slightly dull blades while others find that they require them to be really sharp. Skaters should take notice how they like their blades so that they can get them sharpened early enough (or close enough) to competitions and tests so that they are perfect when the time counts.