Import Bitcoin wallet.dat

An important point to notice if you intend to follow this suggestion:

My mac wallet had 0 coins

If your mac wallet has coins, then don't follow this solution.

First I shut down the bitcoin-qt client. Not sure if this step is necessary but I think it's safer.

Then I copied the wallet.dat file over to

~/Library/Application Support/Bitcoin/wallet.dat Then start the bitcoint-qt client again. It might take a bit longer to startup than usual. Don't panic and let it take its time.