Issues were reported in the beta for 1.6 that were not acted upon. I would expect, as with previous title updates, that an incremental update will be along in a few weeks. That's not even considering what bugs might be uncovered once Dawnguard goes live for 360 users. I would hope that we'd see a substantial title update before Dawnguard is released on the PC and PS3 (i.e. July 26). Personally, I would wait for that unless you have been waiting for things like the navmesh fix, which is included in 1.6.
I would suggest not taking 1.6 entirely, as it breaks the entire Companion questline, even on new games.
It has the
potential to break the questline. As far as I know, there have been no confirmations that it actually
has.