I have used kenko extension tubes with the 70-200 VR, while I liked the results you do need to stop down a fair bit and the AF is practically useless.
You also need to use a tripod and its not a very secure way to shoot as the tubes are the weak link in the setup. I prefer shorter lenses due to the closer focusing difference. Tubes are a lot more versatile than a close up filter, when used stopped down with flash the results can be outstanding!
I prefer ext tubes to diopters, they don't have any glass elements to degrade the image. You lose some light, but it's a trade-off I can handle, having shot large format for many years with the bellows factor.
All the butterflies in my gallery were shot with the 70-200 VR, hand held, and Kenko ext tube (middle one of the set). There is a slight slow down in AF speed as less light is hitting the af sensors, but it hasn't been an issue for me.
Subscribe to see EXIF info for this image (if available)
Extension tubes are a spacer between the lens and camera (with varying degrees of linkages to maintain lens functions). Since it contains no glass it is often said it does not degrade the image. That may be true for symmetric optics like the 50/1.8, short telephotos or macro lenses which work well at close range. Other lenses may show significant degradation since the lens is working well outside its optimum magnification range.
When the primary lens is focused at infinity the magnification is: tube length / lens focal length
You get more magnification with a longer tube, and less magnification with a longer lens. This does weird things when used on a zoom. Normally you "zoom in" to increase the magnification, but with a tube the magnification drops as the focal length increases. The two effects cancel each other out, and ends up changing the focus point and working distance instead. This can be very annoying when focusing manually - and closeup work is usually done with AF switched off.
Diopters or closeup filters are basically a magnifying lens you screw onto the primary lens. Since they don't change any camera-lens linkage, all functions are retained, although I don't know how the change in magnification effects VR.
Most cheap diopters are a single element lens, so are completely uncorrected for spherical abberations (I never heard of an aspheric diopter). While this can create beautiful dreamy bokeh, you also get field curvature and other abberations which affect corner sharpness. Central sharpness usually remains good. This is actually fine for most macro shots (eg flowers) since the subject is usually central and the corners are not in focus anyway. The best diopters are two-element lenses which are much more highly corrected. These retain much better sharpness across the frame. The ones I know of are Nikon's 3T, 4T, 5T and 6T, Canon's 250D and 500D, and Pentax "T" filters. I believe the Nikon filters are discontinued. They can give excellent results, better than tubes with some lenses.
When the primary lens is focused at infinity, the magnification is: lens focal length / diopter focal length
You get more magnification with longer lenses, and more magnification with stronger (shorter focal length) diopters, which is opposite effect from tubes. The working distance of a diopter on ANY lens is the focal length of the diopter, for example, if a diopter has a focal length of 500mm (Canon 500D), it will focus 500mm in front of the primary lens. Not a big deal when used on a 35mm lens, but that's pretty close on a 200mm lens. Diopters work very well on zooms - they stay in focus when you zoom.
If you are looking for closeup options specifically for your 70-200, I'd look closely at the Canon 500D (77mm filter). It gives you 500mm working distance, which is a good amount, and a wide range of magnications from a modest 70mm @ 500mm to a close 200 @ 500mm, and even more if you focus the lens close.
I'm anywhere from 2' to about 5-6' depending on the subject and how close I can get. That's where I feel the zoom is beneficial, takes a little getting used to, but the results are worth it. I've only seen image degradation from me shaking the camera or from subject movement. I use the 20mm (or 25mm) Kenko tube, it gives me just the right working distance, not too close, not too far and I'm not scaring off the subjects. I have to put the flash up on a bracket to get it over the HB 17 hood I use (I use the hood from the 80-200 AFS as it's bigger). The Atlas Moth is the only one I have had trouble with, it's about 9" across, a little too large for this set-up.
I've used this combo with several bodies, the D100, D200 and D2x, works just fine on all.