How widely is taqiyya practiced in the Islamic world?
All Arabs practice taqiyya because it's part of their culture and their heritage. This isn't practiced by non-Arabs though in my opinion.
To the extent you interact with American muslims, how often is it practiced here in the US?
I don't interact with American Muslims but Arab-Americans most likely practice it as well. When I say Arab-Americans I mean Christian, Muslim, and even Atheist Arabs, because all Arabs are unified under a common culture which is derived from Islam, Islamic culture is proto-Arab.
Also, do you see a unification of sunni and shiite muslims in the near future, as it seems Iran and various factions across the middle east would like to have one giant caliphate.
No, that would never happen: Arabs hate Iranians, Kurds hate Arabs, Turks hate Arabs, Kurds hate Turks, Persians hate Arabs, Pakistanis hate Pashtuns, Pashtuns hate Tajiks, an so forth. Also, Islam is dying amongst Iranians because Iranians are becoming more nationalist under the IRI, the more culturally nationalist an Iranian becomes the more they hate Islam. The only people in the Middle East that define themselves firstly by religion are Arabs, because they are the root of Islam, on the otherhand it would be tough to convince an Iranian or a Turk or even a Pakistani to give up his culture and identity over Islam. The greatest gift the Islamic Revolution gave to Iran is that it allowed Iran to have a large population birth and as well see what Islam really was, an Arab religion based on alien culture and alien ideas, the fantasy view of Islam Iranians had was completely shattered.
I suggest you check out Christopher Hitchens thoughts on Iran:
http://www.youtube.com/watch?v=qrBVQjivS08He sums it up
perfectly.