I am not talking about the Win 98 look, but even with the gnome-integration installed buttons look a bit weird and there are sometimes black lines where there shouldn't be any. Why?
This will be improved in LibO 3.4 --see this before-n-after screenshot: https://bugs.freedesktop.org/attachment.cgi?id=42337
It's not using the standard GTK-toolkit - I think it has its own kit... The differences are subtle and many people doesn't seem to notice. But I think it's butt-ugly :/
You can try with a different theme in ubuntu to remove thick black lines though. It's an Ambience glitch.