Turkish aircraft and helicopter gunships have attacled Kurdish rebel positions on the Turkey/"Iraq" (de facto Kurdistan) border, and Turkish artillery has engaged in some cross-border shelling. The White House has (of course) urged restraint.
I find this all somewhat underwhelming. Shelling, and attacks by aircraft and helicopters seem like the minimum the Turkish politicians and generals can do, given the (to a degree cultivated) anger of the Turkish population towards the Kurds. This appears to be a political signal for the Americans, Iraqis and Kurds to Do Something, but, without more, I question whether it is intended to be more than that.
The terrain is extremely rough: and the Kurds have survived Saddam, the Iranians, and now enjoy a degree of protection from Washington. Orbat.com says that the recent Kurdish ambush near the village of Daglica that killed 17 and captured 8 Turkish soldiers was made by a rebel band of about 200. Other reports have slightly different totals of Turkish casualties. The Turkish General Staff reportedly claims that some 32 rebels have been killed in southeastern Turkey -- it is not clear if this occured in this action, or elsewhere. If Orbat is correct: the fact that a band this big can maneuver and get the drop on a Turkish unit doesn't say much good about the state of things on the Turkish side of the border. An excellent topographic map of the border region is here.
The Turks have a big army, which has historically been a good one, but I wonder if they're prepared for what they might find in Kurdistan; or if the government really wishes the political consequences of finishing-off the American alliance ? Quite aside from the difficult terrain and the unfriendly local population, the likely political and diplomatic constraints appear to make a big Turkish incursion a no-win situation for everyone but the most radical Kurdish rebels and the Iranians.