My first impressions are that the noise level is quite low using the buit-in mics.
I have not tested the line level input yet.
When I picked it up, my vendor was saying that he was a little disappointed that "it felt so plastic". He was comparing it to what the D-50 felt like. Now I'll agree that the D-50 felt a little more solid (also twice the size), but if you've owned any of the other small recorders (R-09, Zoom, Tascam, etc.) I think you'd agree that the M10 feels a little more refined.
I think this is the closest thing to a D-8 or M-1 that we've seen yet.