First thing first, how did grinner got on this board, I though the idea was to get away from his type of amateur BS.
Anyway, to answer your question John, my favorite secondary camera is the Sony EX1, if the producer wants tapes then is the Sony Z1. I used my Canon 5D Mark II once just for test but wasn't very happy, mostly because we couldn't feed sound and it can only record for a short period.
Normally we would feed sound to all cameras from the mixer. I have to admit that bringing my MacBookPro with me, having to transfer the files and hand the producer a hard drive is a pain, even thou I'm getting paid extra for it. It's so much easier to just hand over the tapes.
On all E-60 shows we use either of these as an unmanned reporter camera, that's in addition to two HDX900.