Kawasaki, in its infinite wisdom, decided that to keep the price down, they wouldn't waste any grease on the steering head bearings. They probably got a good deal on a boatload of these top bearings with an extra plastic seal so they figured, what the hell. It's a fairly heavy bike and when you get a drop or two of water in there doing it's funky oxide dance with the balls and races you're in trouble. One of the symptoms is the classic 'wanderlust' the bike gets when trying to drive along the straight and narrow going slow - since the bearing will be most worn at the spot it's at when the bike is going straight, this is where it shows up first. Suspend the front (put the bike on the centerstand and wooden blocks under the front of the engine or use a ceiling-mounted block/trolley, making sure NOT to tie up the handlebars or steering head) and check that the handles swing freely left and right. If there's the slightest snag in the middle you will need to replace the bearings.

The shimmy and shake is worse. If, when traveling at slightly above 70 km/h (What? mph? You do the math, Einstein) and let go of the handles, the bike may start to wobble quite violently. Just grab the handles again and change and/or tighten the steering head bearings when your heartbeat is back under 200. The head shake can reportedly also wary with tire wear, tire pattern, bike load and phase of the moon.