I'm looking at used 1DS bodies,
IF you are looking at used 1Ds bodies, I offer the following comments for consideration...
When the 1D2 came out, I still had my 1Ds and I can tell you that from a detail standpoint the 1Ds can out-resolve the 1D2 -- not by much as theyare close, but nonetheless, the 1Ds offers a more finely-detailed file.
IF I were going to consider the 5D, I'd wait and make sure the detail is at least as good as the 1D2 before jumping on it. From what I saw of the uploaded images, I am not overly impressed, yet to be fair they were jpegs. More time will tell. But even at equal imaging capability, I would consider a used 1Ds depending on savings...
...The 5D will most assuredly drive the price of used 1Ds' down further, probably to the $2200~$2600 range.
And let's not forget the 1Ds is a 1-series body, very rugged and well sealed against the elements. (And yes, large and heavy too.) This could possibly make an argument for a used 1D2 if you like the speed and don't mind the 1.3 crop factor, since the 1D2 prices seem to falling too...
Lot's of options.
My .02,