Picked up a couple of these guys today from B&H.
In short - get one for any of your metal-shoed/pin-locking Nikon speedlites. You won't regret it. For more info, read on.
My main lighting setup consists of four Nikon speedlites: two SB-26s and two SB-80DXes.
The reasons I use these lights are:
They were inexpensive - well under $150 (and as low as $100) each on ebay.
They have PC ports on them for use with PocketWizards (or other triggers).
They have built-in optical slave triggers as well, just in case.
Ideally, I'd have a set of four SB-800s, but at over $300 a pop, that's just out of my price range.
I also have an SB-600, the 800's poorer little brother, which does not have a sync port or an optical slave, but _does_ have the ability to speak Nikon's CLS ("Creative Lighting System") language, which can be really useful in certain situations.
Anyway, the majority of the time, I use these lights attached to light stands or other off-camera mounting contraptions. The primary method of mounting a light onto a stand is usually via a bracket, not unlike this one.
I've got a few of these, and some of them came with the exact kind of flash shoe shown in that picture - a little hunk of metal. For my older lights (the SB-26s, and anything older than them as well) which have the all-plastic shoe style, with the screw-down type locking ring, they're fine.
But for the newer, modern speedlites (like the SB-80DX and SB-600), which use the metal shoe with the locking pin mechanism, the metal shoe mounts do not offer a secure platform. In fact, my SB-600 took a nasty spill after slipping out of one of these guys, and is currently at Nikon being repaired.
So I did some research, and found these guys. They are made of a very sturdy plastic - so they won't mess with the other pins on the bottom of the hotshoe. This is significant for a few reasons, including the potential for shorting out the flash, and (at least in the case of my SB-80s) causing the flash to think that it's attached to a camera hotshoe, and overriding the flash's standby and power settings - super-annoying.
So I got a pair of these, one for each of the SB-80s, and they work perfectly.
I think I'm just going to leave the cold shoes attached to the flashes by default, as I always seem to be taking them off and putting them back on again.