My situation is pretty similar to tecmo's. I loaded Windows 7 Pro 64, Internet Explorer 9, Adobe Photoshop applications, NoteTab Pro, Microsoft Office Suite, System Mechanic Pro, and a couple of smaller applications. I was surprised to see how little drive space I used. I wound up using around 28GB of space.
Note - If you are a gamer, the situation changes. Games can use up a lot of drive space. You may only be able to install one game on the drive and additional games on a hard disk drive. You'll wind up swapping games every time you want to play a different one.