And some are very difficult to correct, such as properly incorporating new goods and services. Still, with some heroic assumptions it should be possible to arrive at a serviceable estimate. The Boskin Commission in the United States has put the bias at just over 1%; in other countries, the bias is thought to be no more than half that.
Concerning the desirable level of (properly measured) inflation, there seems to be a consensus that a low positive number (1-3%) is better than zero.1 The reasons for this are both a priori and empirical.