I did most of my 35mm journalism work with Canon EOS cameras, and they became almost second nature to operate on the fly - loved the Canon experience... but wasn't too impressed with the build quality on anything less than the EOS 1 series. My A2 was a great durable camera that had great features and was fast, but it still was plasticy. When I first went digital I bought a D50 because they had a great price at the time for a 'refurb' kit, and the camera just felt so much more solid than the digital Rebels I had looked at. So, for build "feel" the Nikons seemed to have something, at least in the entry level and mid-level camera bodies.
But... there were a number of things that were hard to get used to - attaching the lens, focusing, zooming... all opposite. The Canon command dial in front of the shutter release is so perfectly placed, and the Nikon thumb command doesn't feel as natural as the Canon command dial on the back - which is brilliant in many ways. Also, the command dial on the front of the Nikons is much more awkward to reach for without thinking than the Canons, at least from the perspective of this former Canon shooter. So, ergonomically, I'm still conditioned by my old semi-pro Canon and it's fast reactions.
Yet, I do love the Nikon designs, how the cameras look, how they feel in the hand, and build quality generally up and down the product line, but there are some minor things that I'd change... is it enough to make me switch back? No, it's not. It's probably a bit like learning to drive in England, then having to switch to the other side of the road - there's more to it than just what side of the road to drive on... it's the instinctive things you do when not thinking, and they take a while to unlearn. As I've gotten higher up the food chain (D300) with the Nikon family, I'm suddenly experiencing the kind of instant response and fingertip control of much of my shooting like I did back shooting Canon film SLRs.
In the end, both are amazing product lines. I've been on both sides of the fence, and think this competitive rivalry is one of the best things happening for serious photographers.
The D90 will be an nice choice. Pick up a 50mm f/1.8 lens to go along with whatever kit or zoom you start with - great bang for the buck and will allow you to experience an optically fast lens really inexpensively. This will give you a taste of what fast glass feels like, compared to the typical f/3.5-5.6 zooms most people use.
Good luck, and support your local camera shop if you can. 
