You're totally right nihil ..... even software that recovers data not knowingly overwritten doesn't always recover 100% of deleted data.

I know because recently I deleted photos from my camera and had to run some undelete software. Most of the photos were fine, but one was recovered only half properly. I wouldn't begin to know where to look for data that had been overwritten ... and it's important to remember the distinction between overwritten and having had the chance to be overwritten by the camera or PC being subsequently used. I was lucky that my photos hadn't had the marked "free space" used by more photos (in that I hadn't taken more) but if I knew they'd been overwritten, then I'd have had it.

Just on the business of drive wiping, I remembered this being discussed on an old thread (indeed, I still have your wonderful copy of DBAN Nihil!), where I was told by someone I know to be very knowledgeable that a clean install of Vista would be a completely secure wipe:

It overwrites all data with 0s. That's it. The data is gone for all intents and purposes. The drive certainly can't read it again...
it's technically possible that the old data still "shines through" - as in where there used to be a 1, there's now a 0.0001, and where there used to be a 0, there's now a 0.
However unless you happen to have lost the meaning of life, or the location of Osama Bin Laden on that drive, you're unlikely to get half the scientists in the world working on recovering it.
It was nihil who said:

this is called "magnetic remnance", the other concept is "track overlay", which is where the heads don't write to exactly the same spot each time, so there are traces of previous data at the edges.