Here is a short post on what I’ve found to be the highest quality method for copying icons between things using Finder. As a side note, I keep a folder with icons I wish to retain. It’s just a bunch of folders inside, with each folder having the icon pasted into it, using this method. That way, when software inevitably updates, you can exert your preferences again without having to dig up download links and all that.
You’ll know you’ve copied it right if you open Preview, and hit ⌘N with an icon on the clipboard. You should get a long sequence of crafted variants, as you don’t just want the 1024x. That would look quite blurry at smaller sizes, like in the Dock or in dialogue boxes.
As for 3.4, we pulled the main download link for it on the site because it has a few bugs we really don’t want floating around. So I would stress to anyone finding this thread that the following is provided so you can access the icon if you want it. I wouldn’t recommend actually using this version.