I think there's a few things at play here.
First of all, I think people underestimated the true impact of the Glazer takeover. A few thousand die hard reds haven't been back to OT since, ticket prices have gone up (although no major increase for the last few seasons), the cup scheme was brought in and for many going to matches started to become a chore rather than something you are supposed to enjoy. As a result, a growing detachment started to appear between fans and the club.
Another thing is the players. It has become harder to gain an affinity with the players as there's such a high turnover (how many parents spent big money on Falcao/Di Maria merchandise?) of them. There's also the issues with the wages and behaviour of some. Rooney handed in a transfer request and got a pay increase. That doesn't sit well with many despite what they may do on the pitch.
The funny thing is, I actually started to get more of the buzz back during the Moyes season. That half hour singing v Liverpool at 3 down is something that will stay with me for a long time.
The biggest thing FCUM has done is provide an alternative for the disenfranchised reds out there and despite not being as perfect as some would have you believe, it has achieved that and provides various reds with something to keep their football passion going.
For me, I will always be a Man United fan. You never lose that and will continue to watch them team on TV or at the ground when I can get a spare for the odd game. My main "matchday experience" will now be in the Conference North, that is something that I would have thought was unthinkable 5 years ago.
