I backed up my wallet to a separate, encrypted volume (a .dmg file), and removed the ~/Library/Application Support/Bitcoin directory and replaced it with a link to /Volume/Bitcoin (the new volume) as per the wiki (https://en.bitcoin.it/wiki/Talk:Securing_your_wallet
Now, when I try to open Bitcoin, I get an Exception error, which looks like this:
N5boost16exception_detail10clone_implInS0_19error_info_injectorINS_10filesystem22basic_filesystem_errorINS3_10basic_pathISsNS3_11path_traitsEEEEEEEEEboost::filesystem::create_directory: File exists: "/Users/myusername/Library/Application Support/Bitcoin
bitcoin in AppInit()
Any ideas on what's going on? The image/volume has been mounted each time I've tried to open the bitcoin client.