It seems a lot of computers are switching to solid state drives, and one of the downsides of this is that it seems to make encryption of individual files basically useless, because when you encrypt a file, you can't securely get rid of the original (unencrypted) data. Repeatedly encrypting and decrypting files will result in lots of copies of the encrypted/decrypted files being left on your hard drive for an attacker to pick up.
Encryption of an entire drive is not really a good alternative. I read this paper that says that the key for whole drive encryption can be recovered from DRAM minutes or even hours after a computer is turned off. It's much more effective (not to mention efficient) to encrypt individual files that you want to keep secret, but with solid state drives, I'm not sure if that's really possible any more. Is there any way around this, using solid state drives?