Put me in the camp of liking the HUD's. My C5 vette had it as part of the package and I was so-so on the idea. After having it, you just get used to adjusting your eye focus distance and not having to look down. In my feedback to GM, I suggested making the HUD a dot matrix so other stuff like directions for NAV could be displayed. The C5 UD was a fixed format, so only a fixed set of data could be displayed. I was pretty happy to see it changed for my C6 vette to do that. I don't know why they opted not to put the HUD in the CTS. It is available in the STS & XLR(cough vette), so its not like they did not put them in caddy's. Maybe they thought the pop-up screen removed the need. Dunno. I suspect it may be challenging to retrofit a HUD. The mechanism looks to have a fair amount of depth. I doubt there is that much open space that you could grab under the dash. The display is also very sensitive to the angles involved to get the reflection visible. Just move your head a little and notice it all but disappears from the windshield. So if you do try to install, make sure your going to be able to see it.