Creates on demand backups of Uploads, Themes, Plugins and the wp-content directory. Probably only suitable for smaller sites.
Q. The download times out. A. Your site may be too large for the plugin to handle, I'd suggest you use your FTP program to back up your files.
Q. Is this plugin suitable for WPMU A. No - as is it will allow users to download things they shouldn't have access to. I'd suggest limiting it to just the uploads directory and removing the other options.