The thing I've always wondered is...how do they survive the wind? Anytime I made a permanent stand the wind would destroy it after a few months.
Those anchors that Fitz posted sure would help. You have to go bigger than what you think is needed for support. If you think a 2x4 will work, step up to 2x6 or larger. You basically have to be on the main trunk. Don't tie into branches or the next tree. The wind moves each differently. Don't use nails in the tree-they never last. Don't ask me how I know these things....