Left to its own devices DxO creates a ragged, watercolour-looking file at medium high ISO settings where ACR does this at very high ISO settings. For some reason, DxO gives a better result at higher ISOs relative to ACR. The colour conversion of DxO is generally better than CS3 but with the latest camera profiles, CS4 is producing much better colours. And it does depend on the camera body. DxO is very slow to use, and I am under pressure right now with other urgent work stuff.
But, here goes, before I start on other things:http://www.pbase.com/davidkilpatrick/image/117164998
This shows how the controls of ACR are great for adjusting tones - dodging the foreground, altering colours, burning in the sky with a saturation mask, blurring the sky to limit grain etc; while the controls of DxO (without tonal adjustments) allow straightening of verticals with keystone correction.http://www.pbase.com/davidkilpatrick/image/117164997
This is a close-up at 100% of an Alamy size (17 megapixel 5120 pixel high export) from both, with the DxO lightened in post-processing to reveal detail similar to ACR (which was a bit overdone anway for emphasis). While the DxO image does have higher levels of detail due to sharpening which can not be removed, and the ACR image does have visibly larger noise grains even with zero Sharpness, the DxO image has comparatively high levels of conversion artefacts creating a ragged or posterized watercolour look to edges - the ACR result is technically less 'processed'. Now you may prefer DxO even at the 640 ISO speed, but I prefer ACR. The situation changes at higher ISOs than 800, and the effects are of course not easy to spot at ISO 100-200 with either processor.
I have also put the full size 5120 pixel conversions (photo by Shirley Kilpatrick on 18-250mm and A700 by the way) on pBase, just follow to the next images.
In short, both converters are worth having. If I had an entire set of ISO 100 architectural interiors on a body and lens in the DxO database, which had been perfectly exposed (ideally, bracketed and the best selected for each) DxO would things ACR can't touch. But for a mixed bag of raws needing tonal corrections and local shading, ACR wins.