How important are grammar drills in second language learning?

From the internet. 

Where grammar is given too much priority the results is predictable and well known. ‘Course book’ become little more than grammar courses. Students do not learn English: They learn grammar, at the expense of the other things that matter as much or more. They know the main rules, can pass tests, and may have the illusion that they know the language well. However, when it comes to using the language in practice, they discover that they lack vital elements, typically vocabulary and fluency: They can recite irregular verbs but cannot sustain a conversation. Such an approach is also psychologically counterproductive, in that it tends to make students nervous of making mistakes, undermining their confidence and destroying their motivation.        

Michael Swain (in Seven Bad Reasons for Teaching Grammar – and Two Good Ones).

After reading what was said above, what do you, English language teachers, think about grammar? I am quite sure that no other issue has so preoccupied theorists, linguists, and teacher than grammar teaching in foreign and second language learning.  I am certain that everyone involved in this language learning and teaching context has an opinion. What’s yours? How important are grammar drills in second language learning?