I've been listening to the Bombcast for several years and digital lockers and how they pertain to Ken Kutaragi have been reference dozens of times, but I have very little idea of what that means or where to look for information on that topic. When I've tried to google it long dead post on the Gamespot forums appear of people asking why the guys on On the Spot keep talking about digital lockers on the ps3. So if you have any information on the topic please let me know.
This is all from memory, so take it with a grain of salt.
When Sony was first talking about the PS3 they mentioned that you would be able to put your content in a digital locker and it would age and grow. So, for example, you might put your save in this digital locker and it would give you more gold or experience as long as you left it there. It really just sounds like cloud storage with a few extra features to me, but that wasn't really a term then. I think part of the joke is just how nebulous the concept is. I don't think Sony ever explained how it was going to work. If you're really interested you could go listen to some of the early Hotspot podcasts. They definitely talk about it on there. June 2006 is jumping out at me, but that could be completely wrong.