How big can I print with the D90 and still make it look good?

I have a 30x20 in my lounge that was taken on a 6mp D40. The quality is superb, so lets not get carried away with dpi and resolution. A D90 image with easily print a 30x20 at excellent quality without blinking.

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www.flickr.com/photos/scottbeattie
Nikon D90, Sigma 18-50 2.8, Nikon 70-300VR