CS3 won't directly tell you how many bits/pixel are in the RAW files.
When you open them up in the Camera Raw plugin, notice down the bottom of the screen that you have the option of rendering the file into Photoshop as either 8-bit or 16-bit (and as AdobeRGB or sRGB, etc).
A 10-bit RAW file has 1024 (2^10) possible values for each sub-pixel. But remember that this is RAW data, that needs to be de-mosaiced to calculate R/G/B values for each pixel, and also be converted from linear data and have white balance applied.
In the end, from a 10-bit file you're unlikely to get more than 8 bits of "value" in the final image, even if you render it into Photoshop as a 16-bit file. However, I suppose in some conditions you might get a tiny benefit. If you're doing further processing in Photoshop it can be advantageous to do all that in 16-bit mode anyway (to avoid introducing posterisation in some operations). But if you've done all the "heavy lifting" of the processing work inside Camera Raw (working directly off the 10-bit data) maybe it's OK to end up with 8-bit data in Photoshop!
In fact in CS5 (and Lightroom 3) we can also do automatic lens distortion corrections and accurate colour profiling for the DNG files all within Camera Raw, which further reduces any additional processing.
