Nikon D90 v.nikon D3100?

Nikon D90 v.nikon D3100?

Well they are meant for different types of users. The D90 is meant for Semi Professional/Enthusiast photographers while the D3100 is marketed for entry level users. DXOMark rates the D90 much higher than the D3100 in RAW image quality and other areas. You can see below the results.
http://www.dxomark.com/...2%29/Nikon
As far as total features go, the D3100 actually surpasses the D90 in may ways. Here is complete list
http://www.dpreview.com/...e_post.asp
The most interest new feature is the 1080P recording. Nikon seems to have given it a serious upgrade from the D90 and has included an new auto focus system. The D3100 seems to be a very big move up from Nikon's other entry level models, the D3000 and D5000.It is also substantially smaller than the D90
For me, if it is just about shooting stills, I would get the D90. Its tougher camera meant for heavy duty use and has better image quality. If I wanted something more of a general purpose camera that can take good pictures and HD movies, then I would get the D3100.
http://cheapdslrprofessional.blogspot.com/

The D3100 has no AF motor so you have to be careful when buying a new lens.
It's smaller, lighter, has 2 more megapixels (but same image quality), less noise, better video features and is really great. Both are.
Here's a post called 'Buying a DSLR, what's important, megapixels, features, brand, price, quality and which one to buy - http://www.the-dslr-photographer.com/2009/03/which-dslr-to-buy.html
Good luck! The site has many more tutorials, tips, reviews and guides!