I'm still running 2.1 but it works for me with CS3.
On going to photo/edit in/ps3 the dialog box says that Camera Raw 4.6 is required for full compatibility but gives 3 options. Cancel, Render in Lightroom (which renders out a tiff) or Open Anyway. Choosing Open Anyway opens the Raw file in PS3. Presumably any corrections made in Lightroom which are only available in Camera Raw 4.6 will be ignored. But I can still open the Raw file in PS3.
Running on Mac OSX 10.4.11 if that makes any difference.
Philip
I see no such options with LR 2.2 opening a file into CS3. The dialog box attached is all I see, with only one option whether the file is from a 1DsMark3 (supported in CS3/ACR4.x), or from a 5DMk2, not supported in CS3/ACR4.x.
I don't remember seeing a change from 2.1 to 2.2, but to be honest I was probably already to CS4 by then anyway, and this was the first time I recall ever not having to pre-render a tiff when opening in PS.
The "Open Anyway" option you mentioned might have allowed the ability to open to CS3 via ACR 4.x which wouldn't have required a psd/tiff conversion first, and if LR was writing to .xmp sidecar files, the LR changes would have still been there. But I can't see anyway to enable any functionality similar.
From what I can see with LR 2.2 and later, the only option to open directly into CS3 is a rendered psd/tiff. If LR is writing to .xmp sidecar files, you could certainly open the file from the finder into ACR/CS3 and not have to render the file ... (kind of a kludge I know).
[attachment=12009:CS3Dialog.jpg]