I have a 1t hdd. I also planned on installing xp so I left about 300 Gb for that- haven't done that and now probably never will. I have 500 Mb for boot, 20 Gb for root and about 600 Gb for home. Right now I use 22% of root. I would have to install a huge amount of programs to get close to that 20 Gb. I did have vbox and xp installed last Mint version but that did not come close to 20 Gb either.
i5 3570k, ASRock z77 Extreme 4, 8 Gb Ripjaws 1600, Antec 430w psu, HVR 1600 tv tuner, custom case- marble top, oak face. Carver & DCM Time Window sound system. Mint 14 KDE.