Windows 7 on 4GB
This was running one of the pre rc, 7068 I think. Ive got 7100 on it now and have even more room leftover. probably 900mb free with no problems. I use an 8gb SDHC card for media and some programs.
In my opinion it's not worth the money to upgrade the ssd
if you can do it. Only thing I miss in the vlited version is the games, but I had the old windows entertainment pack from the 90s and now have all the card games back.
I've got skype, firefox, scummvm, foxit and some other essentials.
I use the remote terminal to get into my work computer for any real heavy lifting with office and such.
My mini 9 is just to keep me connected and entertained on a tiny budget.