I have been researching lenses for my new D800 and I have been disappointed by the snobbery that surrounds the D800. Yes its a fantastic camera and of course you should endeavour to get the best glass you can afford for it. So far I have the 14 - 24 and the 28 - 300. I don't agree much with Ken "growing family" Rockwell, but he is right on one thing: I don't care what the charts show, they make me yawn. I don't want to take photos of charts and lines, I want to take photos of landscapes and cityscapes with perhaps a bit of macro and if there is some passing wildlife I'll grab that too.
I went on safari some years ago and I'd love to do it again. What lenses would I like to take with me? A 300 or 400 prime, of course! Which will be most practical? I'd pack the 28 - 300 for sure. I'll be getting the 70 - 200 VRII at some point, but don't want to pay rip off Britain prices for it> I may well also get the 24 - 70, but there are times when you need simplicity.
Yes I could grab a crop camera, but why should I? The only reason I use my Canon 7d (yes I know that's a swear word here) is for extra reach. There are many uses for the 28 - 300. Is it the sharpest lens out there? I'm experienced enough to know that a 10.7x range isn't going to be the sharpest lens. Is it still sharp? Yes it is. In the real world it's a good place to start, yes even on the holy grail that is the D800. Will it live on your camera? Possibly - until you can afford the best glass, but it will be one you hold on to as although it may not be the best glass, it is practical, and not that heavy. Compare it to the Canon 28 - 300L (which I have) and it's as light as a feather.
So to anyone looking for glass for a D800 - don't be a lens snob. Get the best glass you can afford. If all you can afford at the momemt is the 28 - 300, you will still get good results. By all means save up for better glass, but the 28 - 300 is a great lens to have as a walkabout lens, and yes any camera can be a walkabout lens - my 645D is often such an animal. I'm rarely out and about without a camera - sometimes the iphone just wn't cut it.
As usual YMMV.