I've been running Ethereum-Wallet as my wallet on OSX for a while, and it's fine. It's using
/Users/myname/Library/Ethereum as it's data dir.
I've just installed
geth via homebrew with a view to trying out some CPU mining (on the real network, not the testnet).
It, too, appears to be using
/Users/myname/Library/Ethereum as its data dir, yet still needed to download the blockchain on first use.
I am planning to use a new account to mine to, rather than mine into my main etherbase account.
[Update: it appears that geth has found the same account as Ethereum-Wallet, which makes sense if it's the same data dir. So, if I make a new account for mining, that should work - I think.]
Is there a risk I'll kill my wallet? What am I not getting here?