Here’s another article about KDE 4.0. It was published last week, by The Inquirer.
According to this article, KDE 4 uses less memory than the older versions:
According to the German Pro-Linux News, KDE 4 tests showed that it is a substantial improvement on KDE 3.5. The old version needed 348MB to work comfortably while the new one sail through the same tests using only 228MB. In comparison the rival Open Sauce interface GNOME run needs 256MB just for the basics.
Read the whole article.