I'm not exactly sure what Kunin's point is--I thought there actually HAD been a trial as regards Humbert's innocence, that is the entire novel, Lolita, in which Humbert makes his defense to us readers, whom he regularly refers to as his judge and jury; then at the end he finds himself guilty of rape (letting himself off on the murder charges).

I think you can turn Kunin's question about whether or nor Humbert is a "reliable" narrator around a bit. Does his being an "unreliable narrator" mean that he's unreliable about everything? One of my favorite essays by Brian Boyd, "Even Homais Nods" deals wonderfully with this issue. Some readers noticed dating inconsistencies in Humbert's confession and deduced that much of what Humbert claimed to have done most then have been invented. Boyd showed that N. wasn't always perfect in avoiding mistakes in dating; more interestingly he noted that in canceling the basic premise of the narrative--that Humbert had relations with Lolita and Killed Clare Quilty--it also canceled the canceling, making entirely arbitrary which elements in the confession the reader was meant to privilege as "true" and which ones as "false" or delusional since the entire thing originated from the "unreliable narrator".

And I do think N.'s approach in works before Lolita and after show how he tended to have a more or less solid premise with the interpretation of the elements within it up for grabs. For instance, even though the narrator of "Despair", Herrmann Karlovich is insane, I think the reader is expected to think that he existed in the usual fictional sense, was married, did meet a man whom he thought was his exact double and did murder him for the insurance. The reader's job is to interpret the events differently from the narrator, note that Herrman's victim doesn't look anything like him; that his wife, whom he considers dim, loving and loyal is in fact having a rather obvious and banal affair with her cousin, an artist named Ardalion. In N.'s novella "The Eye" the narrator has an affair with a married woman, is caught and humiliated by her husband and commits suicide; he continues to be conscious after death, though, and so to do something becomes obsessed with the public image of another person who lives in his pension (I think). We realize soon that he didn't actually die, that he's crazy, and that the person he's obsessed with is actually himself, even before N.'s reveal toward the end. Then there's the nasty narrator of "The Vane Sisters". Again, the events and people the narrator discusses are accepted as real in fictional terms, but we are allowed to see the characters in our own way, quibble with the narrator: for me the Vane sisters are more charming, glamorous, and pathetic than they are given credit for; we are allowed to see the way they continue to affect his destiny even after they've died, in the message hidden in the narrator's prose. "The Real Life of Sebastian Knight" also has this sort of game going on, with the narrator having biased views that the reader doesn't necessarily share--Sebastian's last Russian Love, for instance, seems to this reader amusing, playful and glamorous; refreshing, iconoclastic and rather admirable--far from the dumb insensitive whore V. tries to make her out to be once he realizes how she shook herself free of Sebastian--really, who wouldn't want to be rid of him?  And this reaction of mine, against the narrator, is the magic of N.'s approach. If you can't trust the ground floor of the premise, though, then the books have no motor, no humor or pathos.

My problem is that in novels like "Despair" and "The Eye" N.' has to bend over backwards to make it so the narrators see everything whose implications they then vociferously deny, so that we the reader can have the pleasant experience of reading "the truth" over their heads. In Lolita, I thought N. finally solved this problem by having Humbert know the answers in retrospect but try to reconstruct his disorientation while experiencing the events for our benefit, to more fully get us on his side. "Pale Fire" on the other hand reverted to the narrator who can't understand the very things he points out for our benefit and suffers a considerable sense of forcing things, as if by artsy jackhammer, into place.

Yet Kunin does have a point: the total destabilization in the narrative she suggests does always hover in the background as a possiblity, like faraway starlight. In Ada, N. gets a genuinely new twist out of his "unreliable narrator" gambit, creating a story whose very premise and events seem always to be in question. Absurdly twinned and twin-named characters, dialogue and inner thoughts that the narrator couldn't possibly remember let alone know, and more strangely to me, the setting itself: Antiterra--why do the people of this world think of themselves as living on Anti-Terra, as inhabiting what is, by implication of the name, a negative foil to our world, Terra, while the majority of Anti-Terrans don't even believe in us?
Here, I think Kunin's way of seeing seems plausible. Maybe Van and Ada really are just cousins in a more banal world that has been overtaken by their folie a deux, a glamorized wonderland where they are almost the same person who love each other happily ever after, though even in this fantasy the happiness can't last and be dramatized without the lurk of its loss.

And Nabokov has played with this sort of thing before too, if not in as drastic a manner: in "Despair" the narrator tells us that he has sent his confession to an author of psychological novels and warns that the writer might try to palm it off as one of his own works; at the end of "The Real Life of Sebastian Knight" the narrator has an intuition that he and Sebastian are one and the same, perhaps someone whom neither of them knows. And Kinbote famously posited the possibility he might turn out to be a happy heterosexual Russian, I believe.  So in answer, I do think at some level Humbert is a reliable narrator--Vladimir Nabokov himself, the precise fatal synchronizer of all his books. And yet--the fun of his books--is that even as they collapse, their dreamy worlds remain intact, Humbert's misdemeanors are bracing, repellent, compelling; Lolita is sharp, funny, courageous, and heartbreaking. Their stories never happened but we give them some kind of enduring reality in our heads, alongside the flow of the real events of our life, which is how morality works, through the creative imagining of others.