Those screensavers that come with Windows 7 have no options that you can set, tweak, and change. If you are the ones who like to use these screensavers and would like to have more control over them, you may want to give System Screensavers Tweaker a try.
System Screensavers Tweaker is a freeware portable app that allows you to tweak and change settings of Bubbles, Mystify, Ribbons, Lines and Aurora (excluded from 7 by default) screensavers.
The tool works in Windows 7, both 32-bit and 64-bit, but requires to have .Net Framework 3.5 installed.[via The Windows Club]