Ah, I had fun with my MP120. It did wonders to improve my handwriting (if you can write so it can recognise it, other people can read it too). Unfortunately, even with the OS upgrade, it was never really fast enough to keep up with a useful writing speed - I was deeply tempted by a StrongARM Newton, which I'm sure were better, but they were even bulkier and always very expensive, so I went to the dark side and got a Palm (if you don't do proper handwriting recognition, you don't need a screen that you can write whole words on, and the device fits in a pocket). Oh, I had a Newton Keyboard, which was a very nice thing to type on - but it was bigger than the Newton and could only keep up with the rate at which the Newton can handle letter entry, which is quite a bit slower than I can type... curse you, under-powered processor. I still think the newer generations were getting interesting when Jobs cancelled them, but then I guess he'd claim he planned the iPad all along.
I'm still very fond of NewtOS, though. The cut and paste (drag to the edge of the screen) was a nice idiom, as was the scribble-to-delete. The concepts of the OS were quite interesting (and different); I only wish I'd had time to do more with it, but it was always on my "must write something" list.
It's a shame NewtHack was so unstable, or I might have bought the full version. Otherwise I really didn't use it much, for all I carried it around a lot. I certainly never used the modem, even though I had one.
I agree about the whining noise. The stylus was very plasticky - I was always worried about breaking it - and it chewed batteries a bit. The little plastic boxes that the rechargable batteries came in were quite handy though - if you want to carry four AA batteries around without leaving them in something (handy for digital cameras, flashes, etc.) The thing I used most, though, was the official leather carry case - in which the Newton rattled about, but a Toshiba Libretto 70CT fits perfectly. I still have it, although I've finally taken to using a mini-note a bit more than the Libretto (even though it's comparatively huge).
My newt got given to a friend, with instructions to look after it. I wish I actually had a use for it.
Two things you really ought to mention in any Newton article: That it was the reason ARM was spun out of Acorn (and all us A5000 owners said "you're doing *what* with it? and shortly afterwards "you're making a computer with the same chip you put in the Newton?" when the RiscPC came out), and, obviously more important, Steven Seagal used one in Under Siege 2.
I probably need to have another play with one. My handwriting's getting illegible again these days.