This Volokh post (via Instapundit) about a former gang member who's been "nominated for a Nobel Prize" prompted me to leave a comment there, which I'll expand over here. It would seem that many people don't realize where Nobel Prizes come from.
The Peace and Literature prizes have a comparatively open nomination process, which makes for what I'm sure is a pretty poor signal/noise for whoever handles their mail. (Of course, the signal/noise of the list of eventual winners for those two isn't so great, either). But the science prizes are run in a tighter fashion. Here's the nominating committee for the Physiology/Medicine prize, for example, and it's very similar for the Physics and Chemistry Prizes.
The various Scandinavian professors involved are notoriously quiet about their choices, as are most prior laureates. The committees never say who these "other scientists from whom the Academy may see fit to invite proposals" might be, and I'm sure that identifying oneself would be a sure way to be dropped from the list. That's not to say that there are no controversies, just that we don't get to hear about them in detail for fifty years or so. That link will let you search older Medcine prizes. It's interesting that the corresponding database searches for Physics and Chemistry aren't even available.
What this means in practice is that no scientist, in theory, is able to be identified as a "Nobel Prize nominee." That doesn't keep it from happening, though. In fact, that link will take you to the story of someone who is claimed to have been nominated five times. A Google search for "five-time Nobel Prize nominee" turns the same person up all over the place. It's almost as if he hasn't done anything to discourage the practice.
One of most notorious recent examples was a neurologist, William Hammesfahr, who was all over the media during the Terri Schiavo case. He was invariably referred to by his supporters as a Nobel prize nominee, but this was another whopper. At least he only claimed to be nominated one time, but anyone who claims to be nominated at all should be under suspicion.
Searching for "N-time Nobel Prize nominee" for various values of N will net you all kinds of stuff. Excluding the Literature and Peace candidates, you find Nigerian crank physicists (more here, medical quacks, and Dr. Johanna Budwig herself, the current record holder in this doofus category. She's usually described by her acolytes as a "seven-time Nobel Prize nominee", which wouldn't be good news even if it were true, wouldn't you think? I note with amusement that in she was being called merely a six-time nominee back in 2002. Things have clearly advanced since those days, which is remarkable since I don't believe that Dr. Budwig is actually still with us.