It does seem as though the system is still in limited testing at the moment and have yet to be made available to the entire spectrum of Amazon.com customers. For those who want to see whether they can be an “early adopter” of sorts, just check out your Amazon address book and see whether you are able to “Search for a Locker Location” and add it as a shipping destination.
It also seems as though Amazon Lockers have made their way across the pond to the UK, where the system is alive and kicking. There is no public announcement of this initiative as at press time, but I would presume that once all the relevant testing is complete with the go-ahead from the top, an official press release will be issued.