Depends on your perspective. From my perspective, not often enough. From my wife's perspective, too darned often.
I always make a minimum $50 purchase just to get free shipping and this has forced me to buy knives I otherwise would not have any interest in. This often leads to some interesting surprises. On my last order I was after a large Vantage Select with charcoal Dymondwood scales. To 'even-up' the order I tossed in an Odyssey, something I normally would not have an interest in. When I got the order and got the two knives in-hand my preferences switched. My reaction to the Vantage was 'meh'; the scales just do not feel right. The Odyssey, however, feels wonderful in the hand and is fast becoming one of my favorites.