The simple answer is no. Screen savers will actually increase the energy used by your PC compared to idle or screen blanking modes. If you want to personalize your PC, a good alternative is to use photographs or other images as wallpaper, not as a screen saver.

With early generation personal computers and displays, screensavers were introduced to avoid permanent imprinting of images on displays during long periods of non usage.  Over time screensavers have taken on more of a personalization role and the need for them has become obsolete due to improvements in display technology.  Screensavers run when a PC is not in use thus they are also energy inefficient as opposed to putting the PC to Sleep or simply using display blanking.  Keep in mind the PC is not in use thus there is no one there to see the screensaver.

Source: Views on Vista