Great tutorial! I have to say, I am also an avid user of inside-out objects - but I agree with others that it's more an inheritance thing than a typo thing. If it was only about the typo issue you could also use locked hashes (well, erm...) or using array refs with constants as indices or something.
in reply to RFR: Inside-out classes - a Class::InsideOut primer
I don't know if you feel like adding it, but there are also some problems with inside-out objects (in general, not with Class::InsideOut, I mean): you have to be more careful about cleanup of the instance data when objects go out of scope, and sometimes it's nice if you can run a hash object through Data::Dumper to debug it.
And the privacy is still relative - I'm not sure how things work under the hood, but wouldn't you be able to step into the package namespace from elsewhere and clobber the hashes holding the instance data?