Yup - me again, sorry... but you sure do know how to ask the fun questions don't you?
By default atm, I believe it's not possible to do this through a setting, but as I said in the other reply - give me time this weekend to plow through the system ok? Initial thoughts would be:
To restrict quantity on Product Detail page
To restrict quantity on Shopping cart overview
Easiest (I hope) will be to override the quantity validator when it is the a product from the specific product type (either thru backend product-type or custom field). This would make sure that no more than 1 product per order can be purchased.
To restrict buying again
If the above idea doesn't work, we're in trouble :) Since at the time of the shoppingcart no order has been created, there's no verification towards the user possible. So this can only happen after the shipping/billing details have been entered. At that moment the system knows if it is an 'anonymous' check out or a 'logged-in-user' checkout.
Anonymous check outs aren't linked to a profile, but for the logged-in checkout, we could back-track purchase history to see if the client already bought this product.
Since it's weekend, I'm gonna dabble with the first and second one, and hopefully have some good news Sunday evening...