I think this is mostly silly. If an attacker can access the data on your hard drive, they will almost certainly have access to your memory as well (and vise-versa). Regardless of where the data lives, it needs to be encrypted. That's the real solution to this problem.
Besides, keeping all your data in memory can have some bad side effects in your application (memory bloat, more complicated code, etc.) This isn't the "right" way to solve they problem.