"Sneaked out" on to the 'net over on Mike Watson's blog - the latest and greatest version of the SharePoint DB Mirroring White paper has must read information on topology support and SQL connection aliasing (intra-farm failover). Async isn't yet included, but nethertheless, this is an essential read.
SharePoint Hosting and Development : The Newest Version of the Database Mirroring Whitepaper for SharePoint has been released