About a week ago, Joe contributed a patch to disable the screensaver on KDE when Miro is playing fullscreen. I don't run any systems with KDE on them. I'd love to get some help testing this patch so that we can include it in the next release of Miro.
The bug for this work is http://bugzilla.pculture.org/show_bug.cgi?id=3067. The patch is at http://bugzilla.pculture.org/attachment.cgi?id=1980.
Let me know whether this patch works or doesn't work for you either in the comments of this blog entry or in the comments of the bug.