OK so, in the interest of being totally thorough... I fired this up on my Windows 7 machine. Worked FINE straight away. No issues whatsoever.
The server GUIs are not the same however. The Windows version does not ask for an IP address, it declares one (whatever the machine's IP is) which is exactly what I expected it should be doing. PS3 saw it immediately and everything just worked.
Mac version however simply will not work, even if I manually enter the Mac's IP address into the server. No dice, Webman will never, ever see anything.
I'm totally at a loss, feeling like the Mac version is just plain broken but I'd love to have someone confirm/deny that!