(sir, a d90 is not an upgrade to the d5100. its a downgrade. inferior sensor, inferior low light performance, etc. just because the d90 is more expensive, does not mean it performs better.)
"Forget the ancient D90, which is a leftover from the previous decade; the D90 trails these (d5100) new cameras in every respect, but costs more!"
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KenRockwell.com: Photography, Cameras and Taking Better Pictures [
http://www.kenrockwell.com/nikon/d5100.htm]
"Snapsort recommends the Nikon D5100." Score: 96(d5100) vs 73(d90)
Nikon D5100 vs D90
I just don't want you to be fooled by the marketing... Heck, the d3100 will even shoot better than the d90. I know because I had both. Sold the d90.