My thought is that the board is pretty important decision and will affect your riding so if you are really into tuning your riding, don't worry about the price. The later you wait, the less sizes are available. You can get like 40% off later on but that's usually the left-overs that no one wants. You can get lucky and be real dilligent about keeping on top of sales but you have to be quick because somewhere, someone will steal from your shopping cart. If it doesn't really matter that much or your dream board is not that popular, then you can wait for deep discounts.
I mean, personally, I don't think the discounts on a board is a significant reduction in the expense of snowboarding. I mean, think aobut it. If you save $100 and you go 10 times, that's like $10 per day. Is it worth $10 to settle for a board you don't really want? Next year, that will be $5 per day. That's like a pizza in the lodge. Unless all you do is street snowboarding...in which case, you prolly want the cheapest possible board no matter what.