I've always felt that at most, you could maybe enhance the service 25% and the food 10% (mainly in regard to portion size) if you spotted a critic. Any more than that and if the critic can't spot that they're getting a dog and pony show at that point, what good are they at judging anything?
But it seems to feed the egos of some media types to imagine that they're so prominent and well-read that they have to do the cloak and dagger routine, all the way to Reichl's disguises (which I love to think were routinely greeted with "Hey, there's someone dressed up like a bag lady on TV at table 7, Ruth Reichl must be here tonight"). Which is why you associate this sort of thing with New York, the Big Ego, more than anywhere else.
People have asked me a couple of times if I try to keep the fact that I'll be writing a meal up secret. Well, I certainly don't draw attention to it, that tends to put people ill at ease, but I absolutely don't think of myself or anyone here as needing to maintain secrecy on any elaborate level because 1) I wouldn't assume people have ever heard of LTHForum (even though it's not at all uncommon to meet a restarateur who has by now), 2) I certainly don't think they'll specifically know me (and that part has proven pretty much true), and 3) even in the unlikely circumstances that I did get some sort of special treatment*, in the next two weeks ten other people are likely to try it and provide a corrective perspective. That is, I think, the significant point about how media are changing-- ten years ago when Reichl wrote a review, about the only response the average person could offer to it was sending in their Zagat vote and hoping that their little pithy "comment" "might be one" "of the ones" "Zagat used." Now we can all put our comments out there, where anyone in the world can read them, and judge all those points of view and different experiences on different nights together as an overall picture. Disguises unnecessary.
* Of course there is one kind of special treatment that we not only occasionally get but actively encourage-- the probing for secret menu items and the like which are then shared with everyone here. In those cases it's not only acceptable but desirable that restarateurs know that someone in a sense represents a community of food fanatics who will be interested in those things, and that we have some ability to get the word out which will lead to at least a certain beginning level of trial and awareness of those items.