zoom lens quality

What about one of those 28-200 or the 80-400 Nikon pieces?
Is that pushing the limits of zoom lense quality?

Is it better to get separate wide angle and zoom or a combination lens?

Advantages, image quality, weight, number of lenses???:)

The more distinct a lens is, the better able it is to cover what it is designed for.

The 80-400 is a dedicated telephoto but slow. It is however an excellent lens.

A 28-200 is technically a larger range as far as field of view. These lenses are cheaper and will not be of such good quality. Instead consider a separate lens.

I've used the 80-400 and it is a very nice lens, but not cheap. The VR is also a great feature in a lens like this, but I'll agree that it's slow to focus. I had a Tokina 80-400 (no VR function) which was about half of the price. In the 80-200 or maybe 300 range, it was as sharp as my Nikon 80-200 f2.8 - really. I have a couple of 16x24 prints from my 6mp DSLR with it that are very sharp. Above 300mm, it wasn't the greatest but that's pretty common among lenses like this. I understand the Nikon is better at the long end but didn't try it myself.

The 28-200 or similar lenses are a compromise. What you gain in convenience you may lose in image quality or focusing speed. If you're not using a tripod, there might not be much difference. I know someone who took a lens like this to Europe on a bus tour and he said that the convenience was great because they didn't have long at each stop. That way he didn't have to carry a big bag and take time to switch lenses, etc. Nice images from it too, but he didn't have any big prints.