I have just encountered this error since I downloaded Bitcoin-Qt version 0.8.5 for OSX running on Mountain Lion, having replaced version 0.8.4 which I downloaded just a few days ago, and am seeing this when I attempt to run it: "Error opening block database. Do you want to rebuild the block database now?". I did not see this error when I ran 0.8.4.

Should I click "Ok" and allow the rebuild of the block database to proceed? Or would it be wise to stick to 0.8.4 for the time being?