It would be nice if it was possible to define the non-standard paths in topology builder instead of a more complex PowerShell method, such as http://technet.microsoft.com/en-us/library/gg398832.aspx
The ability to specify the port number of your sql server as SQL best practice is to change the default port, right now you have to use cliconfig.exe to create an alias to allow it to connect. Also remove the requirement to have an SA account available on the SQL server even though it's not used.
Right now, when you create the mirror, you specify a temp file share for it to copy files to. It would be nice if it cleaned up those files when it was done with them.