In the UK it's both [1]. There's big yellow metal boxes [2] and if there isn't one in the area they deliver to the "7-11" who is probably providing Collect+ [3] type service.

[1]: http://www.amazon.co.uk/gp/help/customer/display.html/?nodeI...

[2]: http://www.amazon.co.uk/b?ie=UTF8&node=2594544031

[3]: http://www.collectplus.co.uk/