Or maybe there is one and I don't know (?)
Anyway, it would be great to have an option in the System Settings list witch would indicate the psp up-time. It shouldn't be so hard, maybe after the first run of the plugin (e.g. after the psp gets the gen-c update) a file would be created with the actual date&time and after selecting the option from system settings, the psp just calculates the difference.
It could get easily hacked, of course, by using a fake date after the system settings were restored or by editing that file but it's just an idea. Someone should make the actual plugin much harder to hack, lets say by encrypting the date&time file or whatever.
And after all, it shouldn't be a plugin for showing off (even if a screenshot option would be nice) but a plugin that lets the owner know how long his psp is turned on. Maybe a "Last stand-by duration: ..." and "Longest Up-Time ever: ..." as well.