Every company is different. The best time to buy is when the get an over stock. The off road world is a little weird. You would think that is when the new models hit the showroom floor but it isn't always that way. You usually have to wait until the manufacturers offer deep discounts to get last years models out of the shops. Unfortunely, the worse the economy the better the deals. If what you want is selling well there will never be a deal to be had.
I know this from buying race bikes for me and my son each year. The best bet is if you don't have any shops that you are partial to, call around. You can sometimes save a few thousand dollars by traveling 150 miles or more. As long as you know what model you want then the machine is the same no matter where you buy it.