Since it has been a while since this topic came up, I will repeat from memory as it is faster than looking for the other thread.
My own recommendation would be to go for a camera that can do something different, not only as a back up but a compliment.
My own back up for the K10D is accomplished by an *istD and a PZ-1. Why you ask?
Because that is the reverse order of my body purchases

,and because they all do something a little different but all work with the same add ons (lenses flashes etc)
Here goes the logic.
All 3 bodies are virtually identical controls and viewfinders, down to dual thumbwheels and program modes. The PZ-1 is new enough that it uses all my AF lenses, and except for my 10-20mm lens all my glass has turned out to be full frame. (something the FF wannabees keep harping on)
The *istD has some great advantages over the K10D that almost no other DSLR has,
- it can do TTL flash, which means you can use K mount lenses and have decent flash metering.
- it goes to ISO 3200 (OK the K20D can do 6400 so you might want to look at it also)
- the manual lens metering is superior to the K10D or K20D so if you want to use old manual lenses, this is really the body for you
controls and functions are similar to K10D (WB adjustment is not as good), and there are 2 drawbacks, which don't bother me, it is slow, once the buffer is full, and it uses CF cards.
If you don't use old lenses, a K20 would be the way to go, if you do, consider an *istD