The maxim of 'managing Street expectations' - a sound principle - is often difficult to follow in practice. Often, a major question for companies is "when" to provide guidance to the investment community, especially to keep expectations in line with the realities of the business.

's bloodletting after its second quarter earnings announcement last week provides a lot of grist for this kind of discussion. The stock was off $11, to $75, after it reported that product sales in the quarter were flat compared to the prior-year period, $251 million vs. $248 million, respectively (