On the D5100: although no revelation, but clear sound improvement over the scabby internal micro! It would still significantly better example with the Rode SVM Pro, but I know myself: let the giant Pracker I would then always at home! The ME-1 is pretty small and light, the "no weight" falls literally!
On the P7700: Hammer! Highly recommended! This Nikon Compact has been with the internal micro-sound-wise in the lead (not only because of "Stereo") and experiences with the ME-1 once a sound improvement. The only fly in the ointment of the internal mics were the strong wind noise outdoors for me. The are the windshield now passe!
Tip: when shooting indoors or if it's really calm, remove the windshield. Thus making the sound a trace is clear!