I have what to say on the Rav Slifkin book ban issue, but I want to measure my words carefully, and so I don't know if I will ever got to posting something substantive on the matter. On the one hand, I would agree with many of the statements labelled heretical, while on the other hand I understand the impetus to declare the boundaries of acceptable Jewish theology. It is a non-trivial subject.
I would just like to point out, however, the contrast between people's reactions to bans/declarations of heresy on that which they agree with/feel comfortable with, and that which they do not.
Specifically, you have Rav Slifkin's views on the age of the universe and the fallibility/infallibility of Chazal when it comes to scientific matters. Many would agree with him (including Rishonim/Acharonim!), and consider attempts to label such an opinion as heretical as backwards and ill-advised.
Similarly, Marc Shapiro's book on the limits of Orthodox theology, which attempts to show that the Rambam's ikkarei emuna (principles of faith) were not universally held or accepted in their entirety, or as understood by the Rambam, is viewed favorably, perhaps in part because it supports privately held discomfort or disagreement with certain ikkarei emuna.
On the other hand, you have messianic Lubavitch, which holds that mashiach can come from the dead, and thus the Rebbe can still be mashiach. They also have sources, admittedly few, and in some cases not well known, but neither are Marc Shapiro's sources entirely mainstream. Yet the same people who would champion the first two would label this belief as heretical, and would write the belief as outside the pale of acceptable Orthodox theology. Dr. David Berger's book talks of the scandal of Orthodox indifference, in that we are not writing them outside of acceptable Orthodox belief, and the same folks who would denounce the idea that an idea could be labelled heretical in the first two cases would agree with, or at least find nothing wrong with, the idea in the final instance.
It is funny to see FailedMessiah.Com promoting on one sidebar Marc Shapiro's book and Rav Slifkin's book, and Dr. Berger's book on the other.