I've just installed WattOS on my 4Gb Mini 9. It's a Ubuntu derived distro using Openbox and LXDE for a GUI. The whole installation left 1.6 Gb empty space on my SSD
(much roomier than the 500 Mb Ubuntu Remix leaves behind).
Some modifications I made after the install include:
Changing the SLIM login manager to GDM because SLIM can't handle automatic logins yet
Adding system-config-printer for my printer (this gobbled up 200 Mb and slowed down my login. The original install logged onto my wireless network instantly after booting)
I added Skype, and upgraded Pidgin to properly login into Yahoo Messenger
After the changes there was still 1.2 Gb left on the SSD
(not including the 400 Mb Swap space which I'll leave until I upgrade the memory from 512 Mb)
There are some issues with configuration panels extending below the 1024 x 600 screen, but applications work just fine.
I tried installing Bastille to harden the system, but it says it won't work with this distro
It's a very nice and tight system with a desktop menu GUI. Great if you only have a 4 Gb hard drive to work with.