One thing for certain - bitcoin private key is far easier to hide than cash, let alone a bank account. However what happens with these bitcoins - if their value plummets or skyrockets or if they get double-spent in a 51% attack (I heard there's been one recently) - that's completely unpredictable.

My opinion - if someone offers you bitcoins in exchange for a yard sale item - take them. But to exchange cash for bitcoins - that's way too risky.