I'm using Ubuntu 9.04 and Kompozer 0.8a3 (ppa version). A feature present in Kompozer 7.10 is (at the moment) missing. When you create a new css style rule, for example a custom rule for an specific #div, Kompozer used to show you a list of identified #div blocks in your page. That was sweet. There were also some very useful example identificators (h1, h2, #header, #body, etc.) in those lists.
Anyway, CSS works right. Its just a feature request.