well, it definitely sounds like you've jumped into the Nikon pool, and I'd advise staying there just for the interchangeability between yours and your wife's camera. only thing that I'd note is that a LOT of lenses (all Tamron, most Sigma, and any Nikon that's not AF-S) won't work on her camera. Nikon's finally changing over to solely putting the AF motor in the lenses, so the D40/D40x are the first cameras to not have the additional focus motor in the body. Just something to keep in mind if you start looking at things like Nikon prime lenses or 3rd party manufacturers.

overall I'd say wait to see the reviews of the new Nikons before deciding whether to pony up the cash on the (higher-end) D300 instead of grabbing a D200 or D80 at a lower cost. I'm not sure that the 200 is going to fall much in price just yet, and also wonder whether the D80 will drop just since it'd put it too close to the D40x.

Lastly, do you have Minolta A-Mount AF lenses? they're compatible with the new Sony DSLRs, so if you have a bag full you may want to experiment with them as well.

enjoy, it's an addiction, but you probably already know that from your film days...