The istD and istDS have the same chip, and will probably have very similar imaging characteristics, though until someone does a direct comparison, thats also not a given.
The istDS looks like it has a dumbed down interface compared to the istD.
This might be good or bad, depending on how you feel about picture taking "modes".
The istDS looks like it won't have the nice feel of the istD.
If you value a solid, nice feeling camera, this might be an issue.
If the camera is just a picture taking tool, and it's esthetics don't matter to you, then it may be a non issue.
The istDS has a larger buffer, and might even write to the card faster.
The istDS supports USB 2.0, and should tranfer data faster during downloads.
The istDS has a wider image parameter control (saturation, sharpness, contrast) from the look of the spece.
The istDS doesn't support TIFF, which bothers me not at all, I never shoot TIFFs anyway.
The istDS won't mount the battery grip. If you shoot a lot of verticals (I do), the grip is nice.
If you are already using a digital P&S that uses SD cards, the istDS uses them.
DP Review has done a comparison of sorts at: http://www.dpreview.com/articles/pentaxistds/ which might be of interest.
William Robb
