I've used the Alpine KCA-420i since it first came out last fall. It has some unfortunate quirks (see this
iPodLounge thread for example), but it's pretty slick. The sound quality is excellent, your iPod gets charged, and you can see track information in the head unit's display.
It's true that it's slow to browse the iPod, an apparent limitation in the interface the iPod developers offered. I just ignore that limitation by preparing a small number of playlists for car use. Or I pick in advance on the iPod itself what I want to play, and the Alpine takes it from there.
The biggest downside, of course, is that you need a modern Alpine head unit (with AI-net connector). In my case, I needed to replace my car's aging head unit anyway, so it was an easy choice.