^ what ultimate said.
Test all of your programs, a few of them object to being moved (or having their System: Library stuff moved) and will demand to be reinstalled and/or serial numbers reinput. You can do that, or you can try manually moving Preferences, Application Support and other items relevant to that application from the Previous System Folder to the live one.
Keep in mind, however, that if it was that program that was crashing your machine, you would be better to reinstall it, than risk moving corrupted preferences and support files into your clean new System.