Here is Evan Kohlmann at CounterTerrorismBlog. Short version: Al-Zawahiri has put his foot in his mouth before, angering even other Islamic terrorists by acting as if groups like Hamas and other Iraqi insurgents are duty-bound to do as he tells them. Walid Phares assesses the whole tape.
Kohlmann also helpfully links a full transcript of the Al-Zawahiri tape and other statements by Al Qaeda leadership.
The tape, of course, was issued just days after President-Elect Obama went on 60 Minutes and confirmed he considers eliminating Bin Laden and the Al Qaeda leadership a “top priority” for American foreign policy.