kakku
I think that I need more than 128 gigs for the system drive.
On my pc with windows 7 ultimate, the C: partition is 55gb used, 33gb of which are for the C:\Windows folder.
Then 10gb for program files and 2gb for program data , 6 gb for Users, 4gb for pagefile.sys and 1 gb for the rest.
Still on the SSD, I have a D: partition with 11gb of programs and an E: partition with 24 gb of everything DAW (including samples) that is not projects or loops.
All this on my 128 gb SSD and I still have 27gb free.
I did move everything I (easily) could that did not require rapid access, to hard drives (no user symbolic links yet).
All of the above will obviously vary from person to person, but it shows that you can get by with a smaller, cheaper SSD.
TreeSize Free is great for finding out where all your capacity is going.