I use CS5 and love it. :p
There have been some additions to the 3D side of things, but I hear CS6 goes even further (and I don't see how that's not a good thing).
I'm interesting in hearing what you don't like about CS5 that you *do* like about CS4.
I don't plan on upgrading anytime soon because they expect me to pay to upgrade to 5.5, let alone 6 only about a year later. And they have been aware of major security flaws in CS5 and earlier versions that the only resolution, in their mind, is to pay to upgrade to CS6. So they have made it onto my shit-list.
But that being said, I don't plan on upgrading anytime soon because CS5 rocks, imo.