My guess is that there is some user error here. a step up from a D50 is a large step and some learning curve is to be expected. read your manual and fine tune everything. also you mention that POS 18-200 lens. not the fastest or sharpest in the lot...
As for the move to a D90, I love mine. once I figured out the controls and software life became easy. I only use live mode when I am shooting low POV and need to make sure my composition is how I like it. after that I turn off the live view, double check the settings and make sure my focus point is where I wanted it (single point)
+1
If you are not familiar with the Nikon focusing system it can seem a little quirky. It does operate basically the same as when it was introduced in the F5. My 7000 has been great, very sharp pictures. I think people just need to get up to speed on the focusing system. If anything Nikon gives you too many options that can easily be confusing. Once up the learning curve the system becomes fairly intuitive. Best of luck to all, and happy shooting.