And how about data that gets swapped out, and placed into a swapfile? Or any other temporary files that get written to disk. The data is still there and you won't know if it's recoverable. If you really need to keep stuff on your personal computer secret, you need to encrypt your whole damn system.
There are third party tools for encryption, but unfortunately booting from encrypted drives tends to be an issue with them. Commercial solutions are available which make this possible, or depending on what you do with your system, you could just have a bootable windows livecd and then have all drives encrypted. Nothing gets stored on the cd and everything'll work fine. There are obvious limitations to this approach, such as difficulty of installing new software. Someone should really research what would happen if all registry hives were to be remounted after boot, to replace the boottime read-only registry with one stored on the encrypted disk.
Either way, full disk encryption is the only way to ensure no data leaks out, and even then some encryption implementations have weaknesses. For example, truecrypt is vulnerable to watermarking attacks, certain specially crafted watermarks can be detected through the encryption layer. That might be really nasty in some cases, but it cannot be used to detect just anything. The data needs to have a certain very special pattern.
As for just removing the data from the system, I wouldn't completely trust it.
PS. Are you feeling guilty about moderating a porn site and don't want your family to find out or what's the deal? Or is the porn so bad quality that you'd be ashamed if someone found out?
