rescue corrupted .nef (photo raw) files

I had no issue opening 4933 and 5180 in Photoshop CS5.5's Camera Raw 6.7. 4938 opens, but does produce the garbage at the bottom as you show. That's in indication that the file is damaged beyond the good image area. With no other file to go back to, there's nothing you can do about it other than crop it off.

Sorry to say, 4951 is hosed.

By "reformatting the card", do you mean you just formatted it in the camera? If so, have you filled the chip up again since then? If not, you can use recovery software on the camera's chip (such as Data Rescue or FileSalvage) to retrieve information that has not yet been overwritten. You may be able to get the original off again that way.

Yup, I always use a card reader. No need to worry about the camera running out of battery power during a transfer (a really good way to lose data). You have to get out a USB a FireWire cable anyway for the camera; pulling the chip and putting it in reader doesn't take any more appreciable time.

I think the problem actually lay with the computer/software rather than the camera.

Yes, assuming you have enough space on the computer's hard drive, it shouldn't be that slow. You may want to consider a few maintenance steps.

1) If you have a bootable install of Snow Leopard on another hard drive, boot to that and use Disk Utility to do both a Repair Disk and a Repair Permissions to the main drive. If the Repair Disk fails, run it until it reports no errors. If after two or three trys it still does report errors, you'll need to use something better, such as DiskWarrior.

2) If you don't have SL installed on a separate drive or partition, then boot to the installation DVD. At the first chance you get (I think it's after choosing a language), go to the menu bar and run Disk Utility there.

3) Remove and reinstall Capture NX2.

These are some of simpler steps before going through a reinstall of the OS.

You might try by-passing the Nikon software and importing/opening with one of the applications mentioned here;

http://www.fileinfo.com/extension/nef

I'd suggest drag & dropping them from the card and then opening them with any of the above, but it may be labour-intensive if there's a lot of pics.

None would do a single actual recovery of files over 10MB, therefore no chance with .nef from a modern camera.

Hmm, unless a trial version was intentionally limiting the size of a file you can recover, there should be no restriction.

The in-camera Format is more of a re-set than an erase.

Correct. It just wipes the file table. The contents are still on the chip, there's just no longer a reference to them. That's where recovery software comes in, as I mentioned above:

By "reformatting the card", do you mean you just formatted it in the camera? If so, have you filled the chip up again since then? If not, you can use recovery software on the camera's chip (such as Data Rescue or FileSalvage) to retrieve information that has not yet been overwritten. You may be able to get the original off again that way.

It's after you fill the chip again that there's essentially no chance of recovering the previous photos. New data has replaced the previous.

Yes, trial versions, but as I have seen others comment, what is the use of a trial if doesn't show anything useful?

The bane of a UNIX system. It's meant to be a secure system, which in turn means it's not supposed to be easy to recover deleted items.

When you delete anything in Windows, its file table entry is simply tagged as deleted. So to unerase them, the tag is removed, which immediately makes the file (or folder) live data again. That's why it works to quickly and easily (assuming you haven't already overwritten the data to be recovered).

When you delete items in OS X, their file table entries are erased. So what FileSalvage and Data Rescue have to do is scour the hard drive for BOF (Beginning Of FIle) markers that the file table entry originally pointed to, which doesn't have a matching starting block to anything that is in the current file table. Once it finds one, it reads the file to its EOF (End Of File) marker and saves it to the target drive. The file name the item had is usually stored in the file header, which it what it uses to give the recovered file the correct name.

Anyway, this all means that the software has to save everything it finds since you can't pick and choose beforehand. The nice part of FileSalvage though is that you can limit what types of files it saves. You can exclude images for example. So when it finds a file that was a TIFF, it knows to skip it. You can exclude a lot of stuff with the various filters the program provides.

Which comes to your issue. The programs are designed to find common file types. FileSalvage has a default entry for Nikon, so it would likely recognize .nef files. For types it doesn't recognize, you can drag and drop custom entries into its interface under the Expert mode. So I could make it recognize .nef files if I wanted to. Not sure off the top of my head if you can do that with Data Rescue.