My completely non-technical gf uses Kde4.3 daily for browsing, email, music, pictures (digikam), watching tv (myth) and finds it okay to use. The only real problem she ran into was with kmail, as one of its bugs started eating all her email before she could read them. (I'm banned from using kmail at work for the same reason). She doesn't change settings much but she knows how to go look for them if she wants something. To her its just another computer like those at her work (Windows XP).
Last year I used KDE, OS-X (Snow Leopard) and XP. I find them all quite capable and usable. Each one has its irks, quirks and annoyances but overall I'm leaning towards KDE. I'm faster (less mouse travel) with KDE on multiple monitors than on OS-X. Its all good however, keep up the good work.