CNN notes that "More American service members have now died in Iraq since the end of major combat than during the height of the war."
It is also worth noting that the Iraq war is now the deadlieast U.S. military operation since Viet Nam, recently surpassing the occupation of Beirut which resulted in the deaths of 254 marines in a single terrorist attack.
The total casualty count in Iraq is now 276, which seems like a pretty small number. However, the rate of deaths "per capita" is pretty high. There are about 125,000 U.S. service members in Iraq, which is also a small number in historical terms. The Viet Nam war lasted eleven years, and involved about three million American servicemen, of which 58,184 were killed (at last count). This is a death rate of roughly 0.17% per year. The death rate in Iraq is currently running at 0.44% per year, or roughly 2.5 times what it was in Viet Nam. (Even if you discount the 138 deaths during the initial hostilities and look only at the "steady state" death rate it's still substantially higher than it was in Viet Nam.)
Is Iraq another Viet Nam? Not yet. But neither was Viet Nam six months after it began.