The latest releases of Tortoise SVN (above 1.6) have taken away the ALT+O hot keys that used to be on every dialog (though it sounds like they’ve added them back in to the trunk). This caused quite an uproar by many keyboarders, myself included.
Until the trunk is stable and the ALT+O keys are reintroduced, though, know that CTRL+ENTER will substitute on pretty much all the dialogs (or ESC for Cancel). These are the “standard” Windows OK & Cancel shortcuts, and apparently the custom accelerator keys are hold overs from legacy WinAPI code.
I’ve grown accustomed to CTRL+ENTER at this point, but I’ll be happy to hopefully have my old friend, ALT+O, back soon.