The full size one like on the main page would work, but something a little smaller wouldn't be bad either. We have a vBulletin forum, but we'd probably use it embedded on our .xml website where staff routinely posts files for our members. It would just make it easier with a Sharecow uploader right on the page and would encourage the use of Sharecow when they upload files.
We would love to use you guys as a replacement for our vBulletin based file attachments and replace the file attachment button with a Sharecow uploader, but the traffic might be a bit much during our peak times. In the past, we crippled a couple of other large hosts during peak download traffic, so we've had to change that practice. ;)