I've been keeping my eyes on this post for a few days, and it is definitely interesting to see the responses. To me, this whole idea can (should?) be broken down into two different kinds of criticisms, style and off-flavors. One of my favorite beer styles Strong Scotch ale, I just love 'em. I've had a lot of Scotch ales where I can definitely smell and taste peat-smoked malt, and I don't like it. Peat in Scotch whisky? Awesome, Laphroaig is outstanding, but I think peat smoke muddies the intense malt sweetness that I love so much in Scotch ale. Would I ever go up to a commercial brewer and say, "You know, you shouldn't add peated malt to your scotch ale"? Absolutely not, because I know my tastes don't suit everyone. On the other hand, if I could taste rubbing alcohol in a Scotch ale, that's a different question and maybe something needs to be said. But I still don't know if I would say anything because the pros who brewed probably have more experience tasting beer than I do, so maybe they already know something went wrong with their fermentation.
Under the right circumstances, "that guy" could be helpful in recognizing fatal flaws in beer that may have gone unnoticed, but "that guy" could also become a nuisance by describing "flaws" in a beer that simply reflect personal tastes. Stone's Arrogant Bastard proudly states "You will not like this beer", and I'm sure a lot of people don't, but the recipe isn't going to change.