Apple posted an updated page detailing their data transfer limits on their .mac blog.

From the page, "The .Mac bandwidth data transfer limit is currently set at 10 GB per month."

The 'add more' options, in Canadian dollars. I've got my own hosting, so I don't need the extra space or bandwidth. The default allocation of 1 GB is plenty of room to back up my purchased music, bookmarks, mail settings, and important documents.