Fred-
It is still doing the DOS (FAT) format header. In fact, you can put the card in your PC, do an NTFS format, go back to the camera, format again and still recover. I have tried doing five formats in a row, with different FAT and sector sizes, then was still able to recover.
I us Photo Rescue which is pretty intense. They do have a free program at their site that will wipe the card.
I believe that depends somewhat on the type of formatting one does. With CF cards you should be doing a quick format, as in the format only touches parts of the disk necessary to declare it newly formatted, leaving most of the card completely untouched. Theoretically a format of that sort could be repeated as many times as one likes without damaging the data on the disk.
However that would not be the case if one were writing to every sector of the disk during the case of the format. While one can theoretically get data back after writing zeros to the whole disk, it does become a more risky proposition and at that point you may or may not be able to recover.
In the case you're mentioning, the key thing is that the filesystem information land in the same place each and every time, as any decent file recovery tool will allow you to ignore the FAT and do a sector by sector search for things that look like files.
