Listen to the opening solo in Santana/Rob Thomas' "Smooth". It will give you a sense of the "flavor" that a maj. 7th imparts on a otherwise mostly Amin. pentatonic solo. Notice however, that the min. 7th is still present, (and its actually the predominant 7th that's played in the entire solo) The maj. 7th is used only for "effect".


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Santana has a tendency to interject maj. 7th as well as flat 5's in otherwise minor progressions as it imparts a very "Latin" feel to the music.
Check out this technique on the "Eagles" "Hotel California"

Hope that gives you some sense of it.