After installing GStreamer extra plugins and GStreamer ffmpeg video plugin from Ubuntu Software Center, it respectively plays mp3 and mp4 smoothly with the pre-installed Rhythmbox Music Player and Movie Player.
Changing a wallaper with a new jpg file edited with the pre-installed GIMP image editor runs satisfactorily. There're also many pre-installed good games too.
Looks like it's the FREE world now, right from the OS up to the pre-installed free applications. They are almost equivalent to, if not better than the commercial software.
I would put it this way, to the level of my satisfaction:
Windows 7 > Ubuntu 9.10
BUT,
Ubuntu 9.10 + free > Windows 7 + $$$
