My Macbook has crashed once or twice daily ever since I installed Lion. I am unable to return to Snow Leopard because my Time Machine is now coupled with Lion.
I went through the sequence:
- Reset the PRAM: Hold down Command ⌘+Option ⌥+P+R on boot. Release after hearing the computer chime twice. http://support.apple.com/kb/HT1379
- Reset the SMC: Shutdown. Disconnect power adapter. Remove the battery. Press and hold power for 5 seconds. http://support.apple.com/kb/HT3964
- Verify/Repair disk Reboot into the recovery partition (press Option ⌥ while booting) and run Disk Utility. The disk had two problems, which are now fixed. http://support.apple.com/kb/HT1782
- Run the hardware diagnostics: Reboot with the original OS X Disk 1 while pressing D. The hardware diagnostics (memory only, apparently) says all is well. http://support.apple.com/kb/HT1509
- Reinstall OS X from the recovery partition: Hold Command ⌘+R while booting. Slight reduction in the rate of crash (but that's only an impression). http://support.apple.com/kb/HT4718
What would you try next?
Edit: The machine is out of warranty and out of Apple care.