I think the turning point for me was the Chelsea/Stoke games.
I've always thought Bobby to be a good manager, but nothing more than that and nothing less than that.
I was pissed off against United at home last year when we pretty let them have a point, but I thought we were improving, especially in defence (with the zonal marking etc). Despite that though, I never called for his head, and strongly defended him when he became unpopular with the defeat at Anfield. I thought he'd get us the FA cup and he did just that.
But this season, his misuse of the fullbacks (especially Kolarov - another player who people are wrong about), his misuse of Adam Johnson, his handling of Tevez and his inability to get the best out of Dzeko all indicate that he's not a great manager. And to do what we want to do, he does need to be great.
But the clown which seals his fate is...well, he doesn't even have to be named. No manager in the world can play a player so out of his depth and expect to get away with it. What's worse (in terms of judging Bobby Manc as a person) is that he plays someone so lazy, so average, so fragile minded, having a pretty good idea of how things will play out, and then when things do play out that way, he tears the boy apart in the press.
It is actually difficult to put into words how incompetent it is to rely on the most unreliable player in the league (world?). I suppose the simile to use is Mancini is like the maths teacher who is quite good at quadratic equations, algebra, trigonometry and all that jazz, but when he plays Balotelli, you realise he doesn't know what 5 + 5 is.
Good luck to him but time to move on and bring in Mourinho.