"The poll is heavily in favour of "vall-ay" (or even "val-lay") over "vall-et"."
At the risk of dragging old meat back to the table (since my servant’s suddenly condescended to open this thread for me!), I am going to stick my knife in as well.
I’m with Max, as corroborated by tsuwm, in that it’s a U/nonU divide, but I think there is also another important process going on which is often seen in language during a period of social upheaval – first, my own pronunciation.
Valet: pr val’it
(and conversely Dr Bill, would you ever hear of a car vallaying service? – certainly not on this side of the pond I think!)
Fillet: pr fill’it
(as already noted, a fish would never be described as other than fill’it’id)
(Linguistic background: raised in Kent, attended private boarding school for High School years, so exposed to definite U-phemisms in a conscious learning pattern)
As caramia notes, she’s “had the 'fillet' discussion with one of the board's antistoecon-inclined ayleurs before, and he insisted that calling them "fill-AYs" was a ridiculously pretentious nod to its french roots...” Indeed I do, and this process is known linguistically as hypercorrection – it is seen in earlier periods of English formation, particularly the influx (hah) of Latinate terms and spellings in the 17th century. In this particular kind of example it’s in charming contrast to the normal American pattern of reducing the language to simpler forms (to produce a closer congruence between the spoken and the written modes, as per the nostrum of dear old Webster). It undoubtedly stems from a population first encountering a new term as a direct loan word in say a restaurant (the French is, as Bridget observed, “a separate word, although cognate” and clearly is “fill’ay meen’yong”). This socially mobile population then applies this knowledge and uses a grand sounding term to a cut of meat when that luxurious cut becomes more widely available, in a form of socially-motivated imitation. The term was otherwise Anglicised long ago into fill’it, and a directly analogous process has occurred with valet. Sure, it was a French loan word originally, but just try applying French pronunciation to the noun form and you will immediately feel why it was Anglicised ages ago: valet’ing the car demands the enunciation of the t sound that would othwise seem awkward and ugly as observed to Bill above.
It’s also worth noting the characteristic slide from the original vowel ‘eh’ before the t, into a more relaxed mouth-position ‘ih’, which ends up becoming almost a schwa: this is the assimilation of the loan word into the vocalization range of the mother tongue. For a characteristic pointer to this difference between native French and English patterns try this example: say a simple English phrase or word, such as ‘superb’, then repeat it trying to allow your mouth to keep almost closed. The chances are you may sound like you come from Birmingham, but it is easy enough to sound it out still. Now repeat with a French word or phrase (in our example ‘superbe’ would be good) – the chances are that you can identify your mouth needing to be stretched over a wider range of movements to achieve a reasonable French vocalization.
