Comment 12 for bug 462407

Aha! I've found it!

On Ubuntu 10.04 its under : /etc/xdg/ubuntuone/syncdaemon.conf

Simply append and mend:

ignore.default = \A#.*\Z
                 \A.*~\Z
                 \A.*\.py[oc]\Z
                 \A.*\.sw[nop]\Z
                 \A.*\.swpx\Z
                 \A\..*\.tmp\Z

With whatever you want. You can add .iso, for example, by doing this...

ignore.default = \A#.*\Z
                 ........---.........
                 \A\..*\.tmp\Z
                 \A.*\.iso\Z

Hope that helps someone out!