1) Fergie must accept it wasn't just the players' fault
Sir Alex Ferguson took the rare step of criticising his players in the wake of their cataclysmic defeat but the great man will know he deserves a share of the blame.
After getting away with a strange selection against Liverpool, Fergie suffered this time for resting Nemanja Vidic in favour of Jonny Evans, who is back to struggling to convince as a United player after a decent start to the season.
Meanwhile Wayne Rooney's favoured strike partner, Javier Hernandez, has started only one Premier League game all season. Why? Danny Welbeck was probably United's best performer on Sunday and at Liverpool the previous week, but he lacks the Mexican's instinctive goal threat.
2) Micah Richards should be in the England squad
On a day when David Silva ran proceedings from start to finish and Mario Balotelli showed there was method to his madness, Micah Richards was a slightly eccentric choice as Sky Sports' man of the match.
There are still worries about his rampaging instincts - seeing the right back in United's box as City's most advanced player with 10 minutes left and the home side threatening a comeback at 1-3 would have done Blues' nerves no good. Some important voices, among them the respected former United youth coach Eric Harrison, believe Richards is not international material and it's certainly hard to shake off the memory of his awful performance in Moscow under Steve McClaren.
But given the way he first nullified Ashley Young and then terrorised the declining Patrice Evra, the fact that Richards doesn't even make Fabio Capello's England squad, let alone the first team, is looking increasingly bizarre.
3) Time to say cheerio Rio?
Rio Ferdinand, the most technically gifted English defender of his generation, looks like a man out of time. Recently exposed by Stoke and Basel, the former England captain suffered another humiliating 90 minutes.
The severity of United's defeat meant Ferdinand had to scrap plans to attend Sunday night's NFL game at Wembley but one senses it won't be too long before he has plenty of opportunity to watch American sports, with the much-discussed move to the MLS surely now very much on the cards.
The next US soccer season starts in March and surely it's not inconceivable that Ferdinand might be in Chicago Fire colours by then.
4) Silva must be man-marked
David Silva has been the dominant force in the Premier League's first nine games and its best player over the last calendar year. Only one team has shackled him effectively so far, and that was Everton, for whom Jack Rodwell did an outstanding man-marking job.
It's hard to virtually sacrifice a player when you're at home, but deploying Ji-Sung Park to nullify the outstanding Spaniard might have paid dividends for United. Silva is simply too good to be allowed to settle into a rhythm but United did that and were picked off as a result.
5) United's soft middle needs fixing
United cannot afford to kid themselves any longer about the deficiencies of their central midfield, where none of Anderson, Ji-Sung Park or Michael Carrick seem able to put together a run of consistent performances and where a lack of both creativity and back four protection created a perfect storm on 6-1 Sunday.
Yes, Darren Fletcher may return to his best form once the effects of his long illness are behind him, and yes, Ferguson's plans to revive the unit have been dealt a setback with the injury to Tom Cleverly. But United should have bought Wesley Sneijder in August and probably still should in January. And it may be time to accelerate the outstanding Paul Pogba's promotion through the first team ranks.
6) Show caution to beat away-day Blues
It's increasingly hard to come up with reasons why City cannot win the Premier League this season. Their deep squad, their abundance of goals from all departments and an increasingly confident defence marshalled by arguably the Premier League's best goalkeeper and central defender makes them justifiable favourites.
But perhaps the biggest factor is the way they perform away, where they are averaging four goals per game. Home teams, eager to impress, are invited on to them in the first 20 minutes and then brutally exposed. The more adventure a team shows, the worse it gets - the two best teams City have played all season, United and Spurs, shipped 11 between them on their home grounds.
The lesson must be for home sides to curb their enthusiasm and show the same discipline as they would while away. Meanwhile, the upside for City is not just measured in league points but in the fact that every lopsided high-profile win against a top team will be noted across the planet, hastening the goal of creating a worldwide fan base which will allow City to keep spending once Financial Fair Play comes in.