I'm running DiabloMiner on a MacMini 10.7 with a ATI Radeon 6630M with the following start parameter:
./DiabloMiner-OSX.sh -u name.macmini -p password -o mining.bitcoin.cz -r 8332 -w 64 -dd

After about 15 minutes the system crashes.

Are the mhash and ghash values realistic?
Last line, before the system crashes:

How can I help to debug the issue? (DiabloMiner works perfectly fine an my old MacMini 10.6.8 that I still have.)

Here is the complete output of the DiaboMiner debug log: (Please notice the increasing numbers for mhash and ghash)
http://codepaste.net/qhr2es