Many SEMs use the tool because it is convenient and Google provides the estimated search volumes. At the same time, many SEMs know how to take Google's estimates and apply them to their campaigns. Experience and campaign history helps SEMs learn this trade.
In fact, did you know that the keyword tool allows you to adjust the type of query based on match type? After you run the tool, you can then click on a drop down menu to select the match type, broad, phrase, exact or negative match.
But the big question is, do you trust the keyword tool? Take our poll:
Forum discussion at HighRankings Forum.