While you'll probably never get cs6 to be as well behaved as cs3 as far floating document windows are concerned, there still a few things you can do.
In time you might find tabs are better suited for photoshop cs6.
1. Set the Taskbar buttons to one of the combine choices
2. In photoshop cs6 uncheck the two choices below for floating document windows
You could set up an action to toggle between tabbed and tiled views. That would give you the best of both worlds.
This represents a fundamental difference in the way the newer versions of Photoshop manage windows. They now employ the facilities of the OS - namely Taskbar Live Previews, which gives you thumbnails. I regard it as better than the old way, where it would park a bunch of meaningless tiny window borders at the bottom of the workspace.
But if you really, REALLY don't want extra thumbnails to show up in your Taskbar (which isn't really that bad, since you can now choose which document you want to work on by previewing its thumbnail), you can enable Tabbed view.
Tabbed view is almost universally disliked by people who are used to using the multi-windowed display from older versions of Photoshop. But try it for a few weeks - it really isn't evil. I know because I once felt that way, and ended up trying Tabbed view for a while. Now I prefer it.