I have Vista x64 installed on a 75 GB partition. I just noticed it was almost full and started snooping around for the space hog. It turns out it's my AppData\Roaming folder. It's consuming nearly half the partition. I don't know what this folder is, but by the name I'd guess it has something to do with roaming profiles. We don't use roaming profiles.
Can anyone tell me about this folder, why it is consuming so much disc space, and how I can get it back?
You need to drill further down to see what's using all the space. Applications you run store data in subfolders of that folder. Locating the particular subfolder that's eating up all the disk space will help pinpoint the application.
An aside: A neat little freeware utility that I like to use to show subfolder sizes, and one that I would use in this instance, is TreeSize Free, available from: http://www.jam-software.com/freeware/index.shtml
Just for clarity, that folder does not specifically deal with Roaming Profiles. It is the "new" Vista location for your Application Data.
As Evan said, check the subfolders to see which Application is writing data there and consuming your space.