https://bitcointalk.org/index.php?topic=337294
Since 0.8.x many MacOS X users have been experiencing periodic leveldb data
corruption issues.  While not fatal, it is very time consuming to recover
from this corruption and upsetting that it happens often for some users.
 There have been three commits in Bitcoin that attempted to fix this, one
fsync fix in leveldb, one in util.h, and a leveldb version upgrade to 1.13.
 My guess is that one of these commits fixed other corruption, but there
remains at least one mysterious corruption issue on Mac where leveldb is
corrupted after a clean shutdown of Bitcoin-Qt.  After 5+ months we still
do not know why some users never see corruption while it happens often for
others.

Gavin has pledged 5 BTC, and Litecoin Dev pledges 200 LTC to start this
bounty.  This thread has public addresses for Mac users to donate to
increase the incentive to fix this issue sooner.

To help please contribute detailed bug reports or links to more relevant
background information pertaining to this corruption issue.

https://bitcointalk.org/index.php?topic=320695.0
For testing purposes, please use either Bitcoin git master or Bitcoin 0.8.5
OMG3, both of which contain all of the relevant leveldb fixes.  Testing
without those fixes will not be helpful at this point.

Warren