I have created a sub-site in my WP 3.1.2 install but I can't access it.
I can see it on the list of sites. If I click Dashboard, I get a 404 error page. If I click View, I get taken to the Great Success! Apache is working ... page.
I checked /blogs.dir/ and there isn't a folder or file there. Not a single one.
When installing the multisite, I added the define('WP_ALLOW_MULTISITE', true); in the config file and then followed the instructions on the Network tab.