I've not heard of any problems with the D90 firmware, there hasn't been an upgrade since it was released. What sort of problems do these people say it has. I bought Nikon because friends already had that marque and so I was able to borrow cameras and lenses to test them out for myself. I have never used a Canon camera but the reviews say they are as good as the Nikon's. Try them both and buy the one you like. I bought the D90 with the 18mm-105mm kit lens first then later on I added the 70mm-300mm and then a Sigma 50mm Macro. Take a look at my Flickr pages for samples of the D90 and lenses.
http://www.flickr.com/photos/deltawhiskey/