Ended up reinstalling. Haven't noticed if it helps with the performance issues yet but I haven't had a chance to get into it much yet. I also had to reinstall Photoshop last night because it's also behaving strangely, so I hope that fixed it. I've lost count the number of times I've had to reinstall Photoshop and I know I've reinstalled Illustrator and InDesign 3 times each now.
I re-installed as well. That fixed the error whilst upgrading to 7.0.3. Now the app shows 7.0.3 in the about box.
But if I check for updates with the Adobe Application Manager (seletc Update... from the Help menu) it still lists the upgrade for ID 7.0.3.
This update really is as messy as it can get. Jeez!
My Applescript was running 10x slower on CS5 than on CS3.
I found that turning off Preferences -> File Handling -> Always Save Preview Images with Documents, fixed the script's speed problem.
Also turning the Display Performance to Fast (Optimized) at the beginning of the script and turning it back to Typical when complete helped for scripts that take more than a few seconds to run.