This isn't exactly a "must have" for maintenance or security etc., but "i" sure wouldn't be without it. ;) I don't use screensavers they don't "save" anything as far as the monitor is concerned. And to me it's just fluff. But i "do" like to change my desktop wallpaper regularly to pics of my choice.
The best prog i've found to do this is Phyll's Wallpaper Switcher:
http://www.philippe.bedard.net/vieux_descr.html
Just use setup by right clicking the tray icon and choose how often you want it to change to another pic(in the designated folder)and it does this and also changes to new one when you reboot.If you get bored with current pic,just click the tray icon and it will switch to another. All you need do is create a pic folder wherever you want(i put mine in Program Files>Plus! on my Win9X machines). Then browse to it from setup and click it then ok out. No nags,no spyware and it's completely free. Phillippe Bedard is a French Canadian IT consultant and just made this and other free programs for people to enjoy...:)
