The following was posted by Thomas Knoll earlier today (19 September)
To answer the most likely questions:
No, this update does not support the Nikon D80 nor the Canon 400D [Rebel XTi] yet. We receieved these cameras too late in our development cycle to make the cut for this release. We understand there are a lot of users now getting these cameras who want support as soon as possible.
There are also a bunch of other cameras models likely to be announced at Photokina which will want to support as soon as possible.
Because of this demand, we are planning to make the time gap between the ACR 3.5 and 3.6 releases shorter than usual, so you will not have to wait all that long for support.
Also, we are nearing completion of the Beta 4 release of Lightroom. This will be released fairly soon (before the release of ACR 3.6). Lightroom is currently in a free public beta program: http://labs.adobe.com/technologies/lightroom
Beta 4 of Lightroom will have preliminary support for both the Nikon D80 and the Canon 400D.
So in the time period the Beta 4 release of Lightroom (soon) and ACR 3.6 (shorter cycle than usual), you wil be able to processor your Nikon D80 and Canon 400D files using Lightroom Beta 4. You will also have the option of using the Beta 4 build Lightroom to convert the Nikon D80 and Canon 400D raw files into DNG format, which can then be used with ACR versions as old as 2.4.