I'm running Mac OS X Lion 10.7.5.
I didn't upgrade from Bitcoin-Qt 0.7.2, instead I backed up my wallet and removed my 0.7.2 Bitcoin-Qt. Then I installed Bitcoin-Qt 0.8.0 (because I wanted to see how long it would take to sync the entire blockchain with 0.8.0).
My new wallet.dat was found in ~/Library/Application Support/Bitcoin and when I replaced it with my backed up wallet.dat all my addresses and transactions showed up.
$ pwd; ls wallet.dat
~/Library/Application Support/Bitcoin
wallet.dat
What files do you have in ~/Library/Application Support/Bitcoin ?
Here's what I've got:
$ pwd; ls -l
~/Library/Application Support/Bitcoin
total 26440
-rw------- 69632 Feb 20 18:04 0.8.0.wallet
drwx------ 3162 Feb 24 03:36 blocks
drwx------ 3162 Feb 24 15:57 chainstate
drwx------ 102 Feb 24 17:28 database
-rw------- 0 Feb 19 19:27 db.log
-rw------- 11991336 Feb 24 17:28 debug.log
-rw------- 909302 Feb 24 17:28 peers.dat
-rw------- 565248 Feb 24 16:41 wallet.dat
Note: 0.8.0.wallet is the backup I made of the new wallet created with the installation of 0.8.0 before replacing it with the backed up wallet.dat from 0.7.2