Apparently the CS3 Design Premium uninstaller is removing a file required for CS4 also.
This is not an isolated incident, as it happened again when installing CS4 on my MacBook Pro. I have also read of similar incidents in other forums. It seems to affect only Photoshop CS4.
Jerry
Its always a good idea to keep the older software around for a while until you get adjusted to the new software.
My point for posting is that there appears to be a bug in the uninstaller and wanted to warn others of my experience.
NOTE: please make a copy of the 'Adobe Unit Types.osax' found Macintosh HD/Library/ScriptingAdditions/Adobe Unit Types.osax
At home did this without making a backup of the 'Adobe Unit Types.osax', so when I launched Photoshop CS4 it suffered from the "Error: "One or more files in the Adobe Application Support folder.."
At work I did this with making a copy of 'Adobe Unit Types.osax', place it back after the uninstall of CS3... and presto so far so good.
for the 'Error: "One or more files in the Adobe Application Support folder... are missing' when you start Photoshop CS4 (Mac OS)" read here:
<http://kb.adobe.com/selfservice/viewContent.do?externalId=kb407726>
sorry if this has already been posted, I could not see this anywhere.