I see you already have another thread going on about zapping the RAM.
Writing zeros and ones to disk, means that hdd space that was formerly allocated by data, and now trashed, will be written over with 1s and 0s, to make that data harder to recover.
If you fear for recovering those bad porn site by someone else, a simple deleting of the trash and the browsers cache (Users/You/Library/Safari or Users/You/Library/Application Support/"Name of the browser") and then emptying the Trash securely (it will be written over with ones and zeros an can be enabled while in Trash and opening the Preferences (Cmd+,) would assure you, that most people won't be able to recover the data, even with software like Data Rescue II (99$).
So why do you think, someone will go trough all the trouble, and recover your web history?
With software it costs money (or not, if the person is adequate enough to find a pirated version) or it will cost real money, if the HDD is given to a professional.
It's your computer, no one else should have access to your user account (if you have accounts set up, and it is indeed your computer).
Good luck.
PS: I will also post this in you other thread, if it's okay. I need the posts desperately.
