NEW INFORMATION

While I think it can be possible if the data hasn't been overwritten, I really wouldn't rely on this.

On the other hand, it's useful to know for the other way round: if you want to delete anything really sensitive, you can't rely on just deletion. You should probably chop your hard drive up, fry it and eat it.

In most cases yes this is true where data is not deleted until its overwritten. When you delete data, your hard drive just takes that area of the disk and marks it as usable space where the data can be changed.