Instead of renaming, my practice has been to remove (using Root Explorer) the apps I don't use from /system/app to a folder called Removed System Apps on my SD Card. That way, I have them and can put them back if I need them for some reason, but they're taking up no internal space.
I've removed the Visual Voice Mail, Amazon MP3, CorpCal, Email, Facebook, Launcher, Alarm Clock, Calculator (I use Real Calc instead), Dock (I use the desk clock), CarDock (I use Car Dock v2), all of the LiveWallpapers and LiveWallpapersPicker, and the LatinIMETutorial, all with no negative effects. I also removed Talk and Talkback (but not GTalkService or TalkProvider, which cause problems if you remove them) for a while, but put them back when I started using GTalk more. I've found that it causes problems if you mess with any of the apks that start with "Google" or end in "Provider" or "Service."