Simple and straight forward thread at Search Engine Watch Forums asks, "Does deselecting "Search Network" hurt my AdWords Quality Score?" The member who posted this thread felt that is may be reducing their quality score, thus reducing the ad ranks in Google.com.
In which, AdWordsRep responds, "Nope."
So simple, opting out of the Google AdWords search network option, does not, in itself, reduce your quality score.
Forum discussion at Search Engine Watch Forums.