They don't just dislike the changes, they despise them:
As someone who reads and observes design quite a bit, I appreciate the simpler design (I hated their miserable navigation before) but I am a bit miffed that they simply stole Twitter's simplicity and built their page into a stream.
I'm unsure of the process that Facebook utilized… first in what motivating them to make the changes and second to push a wholesale change with so many users engaged. I do respect Facebook for taking the risk. There aren't too many companies with their volume of traffic that would do this, especially since their growth is still on the upswing.
It's important to note that change is always difficult. If you roll out a new user interface for an application that people have been using for years, don't expect the emails to come pouring in thanking you. Users hate change.
How did it Start?
I'm looking forward to reading more on the methodology Facebook utilized. My experience tells me that they probably enlisted some power users or a focus group to do the design, paid a big ‘ol stack of money to some human computer interaction and user experience experts, and formulated a plan based on the majority decision. Majority decisions suck, though.
Majority decisions don't allow for unique individuality. Read Douglas Bowman's announcement on quitting Google, it's an eye-opener.
Focus groups suck, don't work either. There is a ton of evidence that suggests that people who volunteer or are recruited to focus groups walk into the group compelled to provide criticism for any design. Focus groups can derail a great, intuitive and radical design. Focus groups tend to bring a user interface down to the least common denominator rather than something new and refreshing.
Why did Facebook Change?
Another question for Facebook – why did you opt for a forced change? It seems to me that the new design and old design could have both been incorporated with some fairly simple options for the user. Empower your users to utilize the interface they'd like instead of forcing it on them.
I'm confident the new design was initiated to remove some of the complexity of the old navigation system. It will be a lot easier now for a new user to get up and running (in my opinion). So – why not make it the default interface for new users and offer additional options for experienced users?
What does Facebook Do Now?
The (multi) million dollar question now for Facebook. Bad feedback feeds bad feedback. Once the survey on the new interface reaches a 70% negative rate, watch out! Even if the design was fantastic, the survey results will continue to go downhill. If I were working for Facebook, I wouldn't pay attention to the survey anymore.
Facebook does have to respond to the negative feedback, though. The irony will be when they offer both choices and the majority of users keep the new look.
It takes additional development, but I'd always recommend two alternatives to pushing change: gradual change or options for change are the best approach.