@choi-- You're right about which word "humdrum" modifies, but xittamarg is still right about the question. Is something "humdrum" going to make you "flabbergasted"? Nope.
Do you see how "advances undreamed of a generation ago" in the second half of the sentence (or, for you grammar wizards, the second clause) is referring to the "galloping technological advances" from the first half of the sentence? Try it with some easy synonyms:
"Really fast progress has made consumers ..........: these really fast advances are so common that they seem humdrum."
And "humdrum" means "boring." So here's what we've got:
"Really fast progress has made consumers ..........: these really fast advances are so common that they seem boring."
Clearly, the consumers feel like the really fast progress is boring. So we need an adjective that could describe the type of person who is bored even by fast progress.
At this point, none of the choices look very good.

But actually, "jaded" in the dictionary has a specific meaning which is slightly different from how it is normally used. According to the dictionary def, if you are "jaded," you are overly accustomed to something to the point where it seems dull or you don't notice it any more. So here it's really a pretty good choice, as long as you know the exact meaning of the word.
Jaded in novels and magazines--or in Aerosmith songs ("Hey, ja-ja-jaded. . .")--usually means what cc411 said: world-weary and bored. We typically use it to describe people who have an excess of luxury or privilege and have become insensible to those things. But that's not the only way to use it, and that's not what it means in this question.