10 gigabytes per month is about 341 MB per day for an average month. It means that, every day you could have 341 visitors per day viewing 9 jpegs in your gallery at 100 kB each (plus associated thumbnails and html/cgi code), or 341 people per day downloading a 1 MB zip file (like you might post at Free Stuff) from your server. It sounds like a safe limit, unless you started getting a higher average hit rate than 341 per day in both site visits and remote downloads.