For contact sync, I use google (macs + various mobile devices). Works fine for me, but then I don’t use gmail’s web interface ever (avoids the auto add problem) as I prefer native mail apps + imap access.
There might be a labs extension you can add to prevent the contact addition/duplication.
I prefer IMAP too but the beauty of it is having access to all the same stuff via Browser as well (and google’s search is often a lot more useful that mail client search as it searches attachment contents as well)
I don’t think the duplication was a browser problem – it was somewhere in the iPhone/apple contacts iSync/???
I know that they’ve made some improvements to contacts but it’s not been rolled out to Apps for Domains yet, only to free customers (!?$)