Should teachers be entertainers? I keep coming across general wisdom of the type, "A teacher has to be a clown". This attitude is gaining traction, e.g. as in this TED talk.

This leaves me quite baffled. Thinking back to my own teachers, the ones I admire most and feel I learnt the most from were all serious and single-mindedly focused. Maybe it is for that reason that I have become a similar teacher, though not by a conscious decision on my part. My students find me a tough teacher but I receive emails several semesters later thanking me.

I have discussed this with colleagues around me and while they agree with me, they argue that the current iPhone generation has so many resources available to them, working hard to grab their attention should also be the teacher's task. Afterall, the argument goes, they may just receive better instruction online through a world leader in the subject.

I am just wondering what others feel about this.
Teachers and professors don't need to be clowns. However, they do need to engage their students.

The old mode of a teacher standing at the front of the lecture hall talking "at" students for an hour or ninety minutes at a time is a cultural relic, rather than necessarily the best way to educate students, as learning in a lecture is usually at best passive. 

There are many ways to get around this problem—including engaging in class discussions, demonstrations, group learning, and, yes, sometimes humor can be used to make the point. But just as teaching should not be a stale recitation of facts, neither is it open mic night at your local comedy club. Learning is serious business, but it doesn't have to be boring, either.