It’s a beautiful thing. I downloaded the ACR 3.6 update (still beta, but seems stable), and the output on the 400D shots is very very good.
As predicted, with a decent RAW converter, the evident noise is strongly diminished, and the noise that remains is very very fine and can be easily removed with Noise Ninja.
Here’s a shot I took at ISO 800 with no flash:
Get the update here: