Ask The Audience is almost always used on the 6th question, like as in 90% of the time.
The Computer Is a Cheating Bastard: Almost every time a contestant struggled between two answers, then used the 50:50 only for it to leave them with (or worse, eliminate) the two answers they were struggling between. It happened so frequently over the years that many viewers complained the "random removal" felt more like rigging (a fact Norm MacDonald caught on to, as mentioned under the Funny Moments tab), especially at the very end of a themed week where the contestant's only options are really Quit or Fail. Several fans suggested to potential contestants that, if they considered using the 50:50, not to say the answers they were considering out loud. The fact that it originally wasn't random (though this wasn't told to the viewers or contestants) doesn't help any — the answers least likely to get picked were always the ones removed, including when Norm was on.
Hype Backlash: The American version of the show is an excellent example of this. The show's enormous popularity quickly evaporated due to ABC's overexposure of it. At its peak the show was airing at least four nights a week.
Germans Love David Hasselhoff: Unlike most of its cousins, the German localization is still running in two weekly primetime slots (Mondays and Fridays) and is still, after ten years, one of the most popular TV shows in Germany. This is partly because of Günther Jauch.
Misaimed Fandom: Despite being the world's most straight-laced game, the UK version has won a number of gongs at the British Comedy Awards.
Nightmare Fuel: The music. As the questions progress, the score gets slower and more ominous, even going so far as to mimicking a heart beat. And, as mentioned in Hell Is That Noise above, the "Out of Time" note is like a Scare Chord straight out of a horror film.
They Changed It, Now It Sucks / Jumping the Shark: Any changes will often vary among the fans to say the least, regardless of the extent or the justification. From Meredith Vieira...to the Clock format...the Hot Seat format...and then the new money ladder...and then "SuperMix"...the announcement of Cedric the Entertainer becoming host...the move to Connecticut the next season with Cedric being replaced by Terry Crews...the replacement of Crews by Chris Harrison after the former hosted just one season...and it goes on. Granted, the show had arguably been in a funk for a while with a dwindling fanbase and thus needed to be freshened up, but it seems each new change alienates as many fans as it reclaims.
Pandering to the Base: In response to the drought, the show created the Tournament of Ten in 2009...but although fans were finally going to get a Millionaire without the need to lower difficulty, they now complained about not only the "manufacturing" of a Millionaire (not a "legit" win by the normal rules of the game, i.e. "answer the standard number of questions right to win"; similar criticism was also leveled against Deal or No Deal's Million-Dollar Missions) but the Tournament's format proving the show was cheap (each seed risked what they already won, with a drop to $25,000 if incorrect), along with the fact that it actually wasn't a "Tournament". The results of the questions proved 'em out, too — nine of the ten seeds, including all but one of the $50,000 winners, decided to walk. Not surprisingly, it was only used that one time.
And now it appears they may be doing it again for the upcoming season by reverting back to the money tree and bringing back 50:50.
Misblamed: Some fans tend to complain that the Sequel Difficulty Spike occurred mainly because the show and its executives became "a bunch of cheap bastards". The actual reason for the increased difficulty is because ratings of the syndicated version aren't as huge as the network version once was (ABC's Executive Meddling didn't help matters), and thus can't offer as much money.
According to Alex Davis (co-runner of Buzzerblog and who didn't like the Clock format), the staff was in a panic during the last episode of that format because there was only $10,000 left in the budget.