Thanks. And, I'd like to give a

to your username and avatar as well. After all, as the wise man himself once said: "I've got the brain of a four year old. I'll bet he was glad to be rid of it."
Hats off to G. Marx - the funniest guy to ever walk the planet!
The problem areas of dark rides and high contrast areas were a mixed bag, however. I found the AF system much, much better, but noise at high ISO is not very good (as has been discussed). In fact, in some ways it almost seems worse than it was on the ist*DL. So while I could AF on things in the dark much better the resultant photos are still very grainy, even if using the coveted 35mm Macro Ltd f/2.8 that I love so much for everything. I'll rent or buy a 55 f/1.4 or similar for our next trip to see if the faster speed helps at all. All ISO levels up to 1600 are fine, but the 3200 is almost useless. I have joked about buying a K-x to use just on dark rides...
3200 shouldn't be useless but the sensor is starting to show its age. The Sony sensor in the K-x definitely works better in low light. Samsung has a new sensor but the relationship between them and Pentax seems to have cooled so who knows what the next Pentax will use... K-x has Sony, K-7 has Samsung, and 645D has Kodak!
If comparing noise vs the DL, I'm guessing that you're viewing at 100%... which really isn't fair when you're talking 14mp vs 6! Still, I was generally pretty happy with the DL at 1600, but 3200 was usually pretty rough, whereas the K-7 can often do pretty good at 3200 and you can get away with 6400 in the right conditions.
As for the K-x... well, just convince your wife that she needs one, and off you go.

I posted some of these in the long-delayed conclusion to my latest trip report, but I'll put 'em here too along with a couple more. These are taken with the K-x with the Pentax 50mm F1.4. 12,800 ISO on the first two, then 2,500, then 10,000, then 2,500.
Now, they don't always look like this - some of the 10,000 and up shots look a bit rough - but in the right circumstance, 12,800 is definitely usable.