I use an app called X-mouse Button Control so I can use my middle mouse button for the hand tool. But if the spacebar is set to play animation then sometimes I will accidently play it, especially when I'm using my wacom pen. It's really annoying and wastes time. Because of this I stopped using CS4 and went back to CS2.
Also in CS4 the taskbar doesn't show when in 'full-screen mode with menu bar.' I wish there was an option for that.