There is a fix for that particular problem. I don't have the wherewithal to find the Blue Post about it, but basically, you have to dupe your computer into downloading the 4G of Cata datafiles that it is missing.
You have to go into your WoW folders under World of Warcraft\WTF\config.wtf and open this file in Notepad. There's a line that says "SetAccountType = BC". You change BC to CT and save the document.
Then--and this is the important part--you open the Blizzard Launcher and DO NOT LOG IN. As soon as you log in, it will change your account type back to BC (burning crusade) and you have to start over. Instead, just sit tight and let it download the 4G of client-side Cataclysm content that you're missing. You might want to set this to run while you're doing other things or sleeping, because you -cannot log in- during this or it will stop.
Once all the content is DL'ed, you can log in as normal. It will change your account type back to BC automatically, but the data files that you were missing (which was causing you to crash when they were called by the system) will remain in place, and no more crashes!