We're running WPMU with subdirectories. Occasionally we have a user who mistypes the URL for an existing blog and requests a blog that doesn't exist. WPMU helpfully tells him the blog doesn't exist and offers to let him register and create it.
This is confusing to users, and some of them go ahead and create blogs without having any clue what they're doing.
We would like to prevent users from automatically being presented with the signup page if they request a non-existent blog. Any suggestions?