So I'm turning an existing WP SU install (upgraded to 3.0) into a network. And I get this message:
Because your install is not new, the sites in your WordPress network must use sub-domains. The main site in a sub-directory install will need to use a modified permalink structure, potentially breaking existing links.
I'm fine with subdomains. But what exactly does the rest of the message mean, and how do I know whether or not existing links will be broken? The site on the main domain has existed for years, with WordPress in the root, and I want to avoid changing its permalink structure (which is simply /%postname%/ currently, BTW) at all costs.