A note on permissions from the Typo README:

"Typo needs write access to several directories in order to function correctly. These need to be writable by the user that runs the Typo process--in a hosted environment this may be your user; on dedicated systems it may be something like 'httpd' or 'www-data'.

The specific directories in question are 'log/' (and everything underneath it), 'cache/', and 'public/'. Strictly speaking, Rails will continue to work if public isn't writable, but Typo's page caching code will work properly and this will cause Typo to be slower and use much more CPU time. For the security conscious, Rails really only needs the ability to change a half-dozen files and subdirectories under public/, ask on the Typo mailing list for more details.

aka...

cd /mytypoinstall
mkdir cache
chmod -R a+rw cache
chmod -R a+rw public
chmod -R a+rw log

Done.