I have the Nikon D100 and as of yet haven’t used the raw plugin but I’ve used the sampler tool with other image formats to fine tune color selection. A quick search through Photoshop’s Help viewer (F1) using “sampler tool” as keyword will give you some idea on how to use the tool. See using histogram and RGB levels in camera raw.

Here are some online examples:

Q&A

Quick sampler tutorial (not camera raw)

Long winded video explanation of the RAW plugin in Photoshop (timed @ 10:00)

Brief video explanation

Hope these help.