I can't really add anything of any value here other than to say that I am a Nikon boy who went to Minolta!
Like steve I have nothing to add, but that never stopped me before...
I'm a Minolta boy who wishes he'd have stuck with it, but there was 10 years between the two and in that time the newer Minoltas seemed a step down from my old XE. I think the (MD) lenses were every bit as good as the nikkor (AI/AIS), but there is so much more selection with a nikon and the new Micro 60 and 105 are the absolute shiznit.
Avoid the "G" lenses. All of the other Nikon AF lenses and flash units work superbly on your N90s body. I usually grab my F100 bodies, but I really like my N90s bodies. Very well designed and built. I've also found them to be well sealed against the elements. And the SB-24, SB-600 & SB-800 work great on them.