Since I just picked one up and having not seen many satisfactorily thorough reviews of this lens mounted on a D800 (I suspect because it's a rather wide focal length for macro work, which I'll get into later), I thought I'd throw in a penny or two worth of my opinion on this lens.
Sharpness (to get this out of the way) is brilliant. At 1:1, I can almost distinguish individual plant cells in shots of my favorite subject (dawn redwoods). No one disputes the sharpness of this (or most any other true macro) lens.
I really want to comment on some of the complaints I've seen of using this lens for macro work.
A quick recap of complaints I've found in other reviews of this lens:
1. You have to get too close.
2. Heavy vignetting
3. Not built well.
I'd like to make a few comments about these complaints. First, they are all true in their way, but there's more to it than that.
1. You have to get too close.
Yes, you have only about 2-3 inches from the front of the lens to the subject when you're working at full 1:1 reproduction. If you shoot bugs, either make sure they're dead or shoot them first thing in the morning when they are still mostly inactive. Don't try to shoot black widows at all. If you shoot inanimate objects, the 2-3 inches isn't a big deal. But won't you get in the way of your lighting? Only if you aren't creative. One quick caveat to add in here. Previously, for macro work, I'm used to extension tubes and reverse rings on non-macro lenses. 2-3 inches seems like endless space to me. So, all things are relative. If I were going from a 150mm macro lens, I'd probably feel different.
2. Heavy vignetting
This is true at f2.8. That's all there is to it. Does this bother me? No. Not really. Not most of the time. I often burn the edges of frames. Heavy vignetting on this lens mean less work for me in post for most of my applications (and lens vignetting usually looks much more natural and pleasant than software vignetting). Are there times I don't want this? Yes. Fortunately, the D800 has so much dynamic range, I have some room to correct this in post if I need to. By f5.6, vignetting is gone. And most macro work is done stopped down to get as much depth of field as possible.
3. Not built well
Meh. It's not a $1,500 lens. The 35mm 1.4 lens feels fantastic. It's metal. It's solid. It's precise. It has a super smooth focus motion. It also costs a ton. This 60mm macro lens is not. It costs $550. For $550, it is very well built. It's not heavy, but it does feel of heavy glass and some metal parts. It is weather sealed. The rubber on the focus ring feels nice. It's focus motion feels good, but not great. The outer material is plastic, but it feels relatively durable compared the plastic on any of my D lenses. Also, as far as the build, the lens is best used for small to medium sized products/objects in a studio setting. It's built well enough I'd be comfortable, yet careful, taking it in the backcountry. But realistically, most of the time this lens will be used in a studio where it will be safe from bears, drops off a cliff, jagged rocks, bull moose, etc.
Now, the positives:
1. You have to get close.
60mm is a great focal length. Practically speaking, the wider the lens, the more depth of field you have to work with. When you are shooting tiny subjects, depth of field is huge. Also, I thought getting close to your subject is generally thought of as a good thing. I've started using this lens as my everyday normal focal length lens. I only really throw my 50mm on if I need to shoot in absurdly low light. 60 is not a bad focal length for portraits (it's not great, either) in a pinch. It gives a slightly more cinematic feel as a normal lens than does the 50. Really, even thought it's intended to be a macro lens, it works pretty well as an all-purpose lens.
2. Less chromatic aberrations than the 105mm.
Or so I've read. I haven't shot with the 105mm, so I won't say much on this and what I do say, take this with a grain of salt. Test and review sites say it's less. I don't know. What I do know is that chromatic aberrations are very limited in this 60mm lens and take very little work to correct.
3. It's sharp.
Just plain sharp. It's capable of resolving high levels of detail, which is exactly why you got the D800. It's hard to produce lens flares. Distortion is almost non-existent (not completely, but almost).
Long story short: It's a great lens. And cheap, too. It's great for copy work and slide scanning. It's great for product photography. It's great for most macro applications (just not dangerous bugs, so no black widows and no poison frogs). And though it's not a portrait specialist or a landscape specialist, it's pretty good for these and other general applications. If you are just wandering, you can feel fairly comfortable leaving most of your other lenses at home most of the time, unless you're going to be shooting something specific and need a specialist lens. It's like having a slowish, but sharp, normal focal length lens, but not having to worry about getting too close for it to focus.
D800: For the D800, in my opinion, it's definitely worth it. It has enough resolving power to impress. With the D800's low-light ability (or a D700 or D3, D4, for that matter), this lens is transformed from a short-ish macro lens into a short-ish macro lens plus a very good normal focal length, casual walk-around, all-purpose lens. All for $549.
*Update: One more quick comment. Its autofocus is reasonably fast (at least as fast as my 50 1.8D lens, maybe faster), which I find fairly impressive given it can focus from 2 inches to infinity. The only problem is that on occasion, it gets lost and has to hunt (and on those occasions it seems remarkably dumb). Most of the time it's great. I find that the times it gets lost are when you've been focused at or near infinity and then you suddenly shoot something at 1:1. Just a quick turn of the manual focus ring tends to set it straight. Like I said, though, this is not usually a problem. It's important to be aware of it just in case, but I have yet to really miss a shot because of it.
*Update 2: Like I said, don't do this with this lens.