Restoring file associations through the default methods like you suggested Roger does not work for all the Adobe programs affected by this bug. In fact I am sure all of us tried doing that... which is why we are on here trying to figure out why something so simple and easy is not working. Illustrator being a perfect example. No matter how many times you try to tell the OS to open an .ai file with Illustrator, it will not. The only solution I have found for this is to run a CCleaner or another type of registry cleaner. This seems to yank out all the corrupted file association registry entries (presumably from CS3) so you can then once again manually replace them with the proper program associations.
CCleaner did the trick for me too!
But I still suspect something about CS4 installer is not right.
Under CS3 I used Vista "open with">"choose program">"always use" to assiciate bridge CS3 with my canon camera raw files.. At that time it did work.
After installing CS4, I wanted to do the same with bridge CS4 but it didnt work. In the "choose program" vista menu, whatever I was doing, I couldnt select bridge CS4 it was always comming back to photoshop cs4 or bridge cs3.
After using CCleaner, I could re-associate the way I want right away.
So my word to photoshop's installer developper: please try to reproduce this issue, it should be easy, and make the installer avoid this.
I had the flip side show up in that uninstalling CS4 required me to re-associate the files to CS3 Photoshop. I'm told this is SOP for backwards compatibility, although I don't know why it should be so.