OK, here is my take on this. I also have the 24-120 F4 and I'm also concerned that I may not get as sharp images from the D800 as I do on my D700. But I think it's how you determine what sharp is and what media you are outputting to. Most of my shots end up on the internet and a few get burnt to a disc at hi-res for future printing. I'm not too worried about the internet shots, I'm sure I'll get nice crisp looking images from the D800 after downsizing. As for the hi-res printable images, I'll have to be more careful when taking these. On my D700 I can get away with shooting hand held images at 1/100 second at 100mm without the VR on, but I doubt I'll get away with it on the D800. I think with good hand holding technique and a higher shutter speed than I'd normally use will be the ticket with the D800. I shoot a lot of models with off camera speedlights at focal lengths between 24mm and 150mm (my 24-120 F4 is my go to lens for this) and I don't think I'll have to change much here. I normally shoot at 1/200 second for indoor/studio work and rarely go below 1/100 second for outdoor shoots, depending on ambient light. I have no intentions of using a tripod for the model shoots, they are moving just as much as I am (shake wise) and the flash "should" help freeze any minor movement. I will start off shooting the D800 like a DX camera, where shutter speed should be at least 1.5 x the focal length or higher. I very rarely use a tripod and I'd like to keep it that way! But when I do use the tripod, I normally use a shutter release cable and exposure delay mode and I'm sure this will work just as well on the D800.
The way I see it is, I have the D800 on pre-order and I do intend taking delivery of it. So I will learn how to use it properly and how to get the best out of it.