Sony had some interesting comments regarding people who own UMD versions of games. They're working on plans to allow owners to transfer or download games they already own onto the PSP Go. That would be a nice nod to existing owners. May create a mini-run on the used market as well to get games for cheap that then would be transfered to the PSP Go.
Kotaku - Sony Is Working on a UMD Solution for PSP Go - E3