I started writing this for the consensus list, but it got long and I still had more to say, so I decided it would be more appropriate to put it here.
Personally, I sometimes wonder if niffweed's type is one of the forum typings that has been taken for granted, even to the extent of having become part of what some people's idea of ILI's is. I'm not saying that he is or isn't any particular type, but I want to remark on a few things.
Temperament: IP's are observers above all else. Their experiences are often largely defined by their observations. That's why they're "relaxed, go with the flow". Niffweed doesn't strike me as being being at all "go with the flow". Rational types have ideas about the way reality should be, and they try to shape reality to it, or at least complain about where it differs. While niffweed isn't the most proactive person, he certainly doesn't seem to be primarily an "observer". On the contrary, he seems to like to ruffle feathers. This is a rather un-IP trait, imo.
Ni: There are things about him that are not consistent with a typical Ni dominant. Ni dominants generally have a feeling about them of being not quite in the moment entirely. They're often detachedly reflective and see hidden connections between little things that most people, including Ni creatives, wouldn't have taken the time to consider. If you don't know them well, they may blend into the background. If you do, they're likely to have an unusual, slightly surreal take on most things. They're attracted to abstractions and enjoy discussing oddities. Being observers allows them to notice and comment on things that break the flow of events, and they may point out things they see as unusual or unexpected. Their analogies are more focused on imagery, symbolism, and abstract concepts than most people's. I've considered that some ILI's have less apparent, less... stylistic?... Ni, but it's difficult for me to overlook this aspect of typing him entirely (seeing as how it is considered by most to be his dominant function). On the other hand, I want to make it clear that the presence or absence of strong Ni is not by any means one of the main reasons I'm doubting his being ILI. It's actually one of the less significant reasons.
Se: Taking the "less apparent Ni" possibility into consideration, his being an intuitive type still doesn't entirely make sense to me. I don't see weak Se. All of the ILI's I've known have appeared rather dispassionate most of the time. From a distance, they all come across as being somewhat passive and unobtrusive. The dual seeking function and PoLR are the weakest functions, the functions that we're totally helpless in regards to. Niffweed does not strike me as being helpless where Se is concerned. He seems self-possessed, has a strong will, and readily stands up to pretty much anyone. He's also more self-possessed than any Ni dominant I've ever seen. (This may also be partially related to Fi.)
Fi: I'm not sure niffweed has weak Fi, either. Te types usually don't have clearly defined Fi. They doubt whether their idea of what's right and what's wrong, and they don't usually have many strong likes or dislikes for particular people, either (this obviously has exceptions though). While there isn't much evidence at hand showing that he has particularly strong Fi, looking back at some of his interactions, he does seem to have some clear principles that's he's quite confident in and comfortable being vocal about. The things he's assertive about are more related to Fi (or maybe possibly Ti) than to Te.
Te: ILI's are very unassuming in the way they deliver information about what they see as being potential problems. I think that it's quite possible that niffweed is using Se to criticize, and people here are thinking that it's Te criticism (and have for so long that it's become a part of how they see Te in ILI's). ILI's have a very different way of going about criticism. Their criticisms are impersonal. They're about the realities of situation, not about people or principles. Their criticism will more likely be something along the lines of "this could have that negative consequence" or "this won't work" or "that is incorrect" or "this bad thing is going to happen" or "if this would have been done that way, this wouldn't have happened", not "you are an idiot" or "die". ILI's are unlikely to attack people over ideology.
Fe: If ILI's offend someone, it is most likely because they failed to understand that their words or actions (or lack of words to actions) may do so. They don't see catering to people's emotions and or the mood in a room or the atmosphere of a group as something important that should be done, but they don't purposely upset people either, generally speaking.
Ne: I think some people like to think that niffweed's randomness is an ILI trait, perhaps Ni + irrationality. The problem with that though is that Ni is about connections and flow. Niffweed's randomness is too abrupt and... well, random to be Ni. It seems more like bastardized Ne combined with Se. When Ne PoLR types try to use what they think Ne is (even if they don't think in those terms), it can come across as just being totally random.