just curios 120GB is enough as primary drive for softwares/OS?
I use many softwares. Visual Studio 2010, SQL Server 2008, Adobe Premiere Pro, Photoshop, Office 2007.. and a lot of small ones. And I have done that on a 60 GB partition. And I am using all that on a PC installed with Microsoft Server 2008 R2 (which takes a lot of space). To add to that I have also installed Ubuntu on a 40 GB partition, and XP (for some tools) on a 20 GB hdd.
So you can see, I can easily manage triple boot on a 120 GB SSD.
Btw, I have tons of games installed on Steam. But I have mapped, C:\Program Files\Steam to a folder in D: drive created specially for Steam (through a process called, "Mount Point"]. And you can do that for each folder, or even complete Program folder. So there is no reason why a 120 GB SSD should be less if you just want to install OSes on it.