The D3100 has less dedicated buttons and dials (means more menu diving), no auto bracketing, slower FPS (3 vs 5), penta mirror vs pentaprism (smaller, dimmer viewfinder) no built in focus motor and no off camera flash control compared to the D200. (There are more, cons, but these would bug me)
OTOH, the D3100 has better high ISO, movie mode and is signifcantly smaller and lighter, meaning you would take it with you more.
Your call. Personally, I would look at a SH D90 or even D300.
hmmm This is why I'm abit hesistant, Im always shooting in A and M nothing else, if the FN button can work as an iso, and i just have to alter the WB then I'm happy as pie. I really would like a quieter camera and the ability to happily use ISO800, and ISO1600. D3100 does just that. I'm use to rangefinders, and how quiet they are, the D200 is anything but quiet.
But I also have an elinchrom kit, and some other flash, but my friends d60 worked with it... I don't use nikon speedlites... but third party speed rings and what not (elinchrom quadra, etc.)
The AF motor does suck indeed, it means I would have to sell my 28mm D but It should work with my 24-70mm G no? and with the 35mm and 24mm G I'll just get one of them if they work since I love shooting around 28mm.
Viewfinder is important imo, but to be honest, I might get a cateyez later down the track, and I've worked on a d60 before... It would bug me, but not to the point of oblivion, as long as i have my horizontal, and vertical lines.
I moved from a D60 to the 3100, love it. Like you I love small, light cameras. There is nothing to touch the 3100 in this respect
Yeah Ive been shooting with rangefinders for a while i prefer smaller low profile cameras, especially when you're shooting round in dodgy areas. Is the D3100 made out of plastic again though? no magnesium? I assume nikon wouldn't spend much on the body design, but I haven't looked at upgrading since last year...