I put new bearings in when I replace rotors, about once a year. Tighten until finger tight, use a wrench to run just past finger tight to take the slop out, back off and snug it up just a little more than finger tight. If the wheel spins slower after tightening, you've gone too far. When you lift the front for any reason, rock the wheel from top to bottom. Any slop, readjust the bearing. Otherwise its fine. I use redline grease, just enough between the bearings to coat the walls about 1/4 inch thick. Never had a bearing fail.

The rears are self lubricated.