I have evaluated Word-2007 contexual speller and was a bit disappointed. The percent of the out-of-context words recognized was rather low and the percent of false negatives was very high. Suggested corrections was rarely appropriate.
My suggestion for the respected public is to look at Ghotit on-line speller, which up to my knowledge provides much better results. Note, that I am proud to be associated with Ghotit, being one of its developers.