Head bolt torque is very important, as is intake manifold bolt torque, and most all internal engine things
....Otherwise, I tend to do everything else (outside the engine) by feel. Feel can get you in trouble too though, especially with bolts that have been heat stressed, like exhaust manifold bolts. They tend to break rather easily if reused or even slightly over tightened. Same thing with bolts smaller than 10 mm. And like Ish said, you don't really want to mess around on an aluminum block. Some places are impossible to fit a torque wrench into, so I usually limit the torque I can put on a small bolt by using a "shorty" wrench, or even 1/4 drive on the really small stuff.