Summary:  Checks a requested new blog’s information against a series of validation rules.

Detail:  This function checks that a new blog meets a number of validation rules before proceeding on to create the blog.  The rules include making sure the new blog’s name isn’t on the banned list, checking that there is a name, that it is alphanumerical, that it’s long enough, etc.  You can pretty much read through this function if you want to check the rules as they are.

You could also use this function to impose your own rules, if you’d prefer hacking the core to creating a plugin.