- It suggests that Al Qaeda in Iraq keep in mind international Muslim public opinion when planning attack;
- Specifically advises to refrain from civilian attacks on Shia Iraqis because other Muslims, even non-Shia, will not understand them (even though they are quite justified to Al Zawahri and a confrontation with the Shia will happen "sooner or later anyway");
- It extensively refers to Al Qaeda's experience in Afghanistan, notably with regards to the collapse of the Taliban regime, to warn Zarqawi about the importance of sectarian and tribal relations--in other words, broad-based support;
- Meditates on the potential emergence of a embryonic caliphate in the Sunni parts of Iraq after an American withdrawal, which it predicts will come soon, but reiterates his view that such a caliphate's true heart is Egypt and the Levant ("a bird whose wings are Egypt and Syria and whose heart is Palestine");
- Of interest to Egypt-watchers, Zawahri talks about an article or book he wrote called "The Muslim Brotherhood in 60 Years: The Bitter Harvest" in which he warns about the "dangerous trend" of appeasement within the Brotherhood.
All this is from a quick glance at the letter, which I'll try to read more in depth later. I'm not sure how credible the letter is (or whether it's been acknowledged as authentic or denied) but if it's real it's a fascinating look inside the mind of Al Qaeda's leading strategist.