That’s the question that UPI’s Martin Walker answers in a recent piece. Reacting to French President Nicolas Sarkozy’s proposal to reform NATO and integrate France fully into the alliance, Walker discusses the possible effects on U.S. and U.K. interests and notes the woeful state of NATO fighting ability at present:

The hard fact is that only the French and British can deploy sizeable forces of all arms quickly with the communications and logistics and air cover to back them up. Germany spends just over 1 percent of gross domestic product on defense, half the French and British levels, and most other EU forces are in similar shape. Their budgets, readiness, training, weaponry, capabilities and support units are nowhere near adequate for modern operations.
The lesson was plain in the Kosovo campaign in 1999, when NATO’s European members with nearly 2 million troops nominally under arms found it almost impossible to deploy 40,000 of them.

There are real consequences of this fecklessness and unwilling to fight, according to USA Today:

NATO commanders are not free to use all the troops that they wish. Some of the 38 countries that have deployed forces to Afghanistan have rules designed to prevent them from engaging in violent situations.
“You’re fighting with one hand tied behind your back” said Seth Jones, a counterinsurgency expert at the RAND Corp, a think tank.