Looks like you can still play games on PSP Go when it's in shuttered mode.
When asked if Sony had any titles in development that would focus on using just the L and R shoulder buttons, a rep told Joystiq that new titles for that specific function have not been announced just yet, but sure.
"Users will be able to access content and applications on the XMB such as videos, music and Skype when the panel is closed -- but users will need to launch the application first before closing the panel, said the rep.
Games that use the L/R buttons will allow "users will be able to play those games with the PSP Go in closed mode" while "original applications" like the clock and calendar will also be accessible when shuttered.
Good to know we guess.
More through the link.