Check out bitsafe. It's a small debian based distro meant for keeping a wallet secure with multiple levels of encryption. You can use it inside a virtual machine.
I am unfortunately not linux-savvy enough to trust myself with it. I only migrated from windows to mac 2 years ago and while I think I have a pretty good handle on the mac, I no longer have the time or the learning ability to get myself confident enough with linux to sleep well at night thinking a good chunk of my savings are on linux. I actually thought about buying one of those small netbooks with linux preinstalled and keep it exclusively for my btc savings wallet, but again, I don't know enough about linux to sleep well. In conclusion, it's going to have to be mac-based.
I actually read about another idea: get a new computer (or install mac on a fresh hdd) and keep it entirely offline. Install the client, generate a wallet, get the receive address and just deposit to it. Check the balance with block explorer. Never bring the new computer online until it's time to spend btc's. There's one problem: I need to be absolutely confident I can get the btc's out, and that means bringing it online to do a trial spend, and repeat occasionally. At that point, the computer might be vulnerable to trojans and such, right?
Thanks for the tip though, Red, I appreciate it.