So I ran a quick comparison test between the DPP HDR and the Photoshop CS3 HDR using 3 5DC CR2 files. My main issue with the DPP tool is that it tends to fail at auto-aligning where you haven't shot with a tripod, at least on my three tests over a couple days it failed on two, whereas CS3 handled each.
The are some usable controls in the DPP HDR window, basic global contols but you don't have one as fine-tuned as the CS3 White Point setting. However you do have global Brightness, Saturation and Contrast, and a nice Digital Enhancement feature which among other things can do some pretty hefty sharpening, and also a little "Art" dropdown list where you can choose one of those "artsy" looks.
Then. CS3 gives you Adjustments in the 32-bit image as well as a nifty "gamma control" when you are converting to a 16-bit image. DPP doesn't have that ability. You Save As and get a jpeg.
However, you can do some adjustments in the Tone Curve control, which can have the end results that are similar to the final outcome of CS3. However, the default settings of DPP emphacize the highlights more than I'd like, so you do need that final Tone Curve adjustment.
So, my take is that DPP is quicker and simpler, and as long as you do the Tone Curve tweaking, has a decent output, however, you may not be happy trying to use it with hand-held shots!
If anyone is interested, I could post a project in the HDR forum, let me know, otherwise I won't go to the trouble
!