I use Arch Linux and gnome 3.6. In smplayer 0.8.1-1 there is an option to disable the screensaver, but it does not work.
The tick box is checked by default but still it doesn't work.
SMPlayer > Options> Preferences > General > Video > Disable Screensaver.
Steps to Reproduce:
1. Open SMPlayer
2. Load a Movie
3. Wait.... wait... SCREENSAVER.... (ruins the movie).
But vlc works fine.