Sorting out X problems can be a headache. The breadth of issues is wide and the complexity can be deep, so it's always helpful to have some where to turn to when you need deep X know-how. Fortunately Bryce Harrington has created a set of X Troubleshooting Wiki pages which have proved helpful to fix X issues.
The wiki covers a range of topics, including: Resolution issues, high CPU utilisation, blank screen issues, freezes, font sizes, X resume crashes, Intel performance issues and hotkey fixes to name but a few.
I'd recommend you to check out the Wiki even if you don't have X issues, just because it's packed full of useful X config nuggets of information.