I was waiting for these... I thought about upgrading over the weekend too, but figured there had to be some issues...
Have you tried deleting your preferences? Is it possible that your last export was to a location that under 10.6 is no longer there or something like that?
where do I delete these at?
HD/Users/(Yourname)/Library/Preferences/Adobe Illustrator CS4 Settings. You can dump the whole folder or alternately if you have a lot of custom settings, move the folder to the desktop and restart AI. It will recreate the whole folder.
Deleting the preferences will do it but while you are there I would also delete the com.adobe.illustrator.plist which is also in the user's preferences.
If you have other Adobe products this might be necessary for some of the other applications.
There is one thing that seems to have been lost the ability to drag and drop a jpeg file from the desktop or finder to an open Illustrator document, you can still drag and drop a tiff or photoshop file and that is the same.
Putting that aside Smow Leopard makes Illustrator and other Adobe apllications faster in general and seem promising.
To give you guys an idea my Mac boots in one minute with all of my login and haxies installed that start at boot. It use to take 4 minutes.
That is a big improvement.
I read about printing problems but I thin those user would be wise to remove their printers from the printer list and then addthem back while running SL.
They may become happier campers.