Why does everyone want to reassign command-space all the time? Since System 7, command-space has been for switching input scripts. Now it clashes with Spotlight, Butler, Quicksilver and even Safari! When will the madness stop?

The madness is in having the default be input method switching.
This key combo is way too good to use for something like that (and yes, I do switch layouts. It's just that I don't need a key for something I only do a couple times a day)

Your primary input method is single-byte Western European, isn't it? If you have to use a multibyte or Unicode keyboard layout/input method, you'll find that OSX regularly switches you back to a Western European keyboard layout for no apparent reason. You're constantly having to switch back. Command-space is convenient for something you have to use every few minutes.