The biggest problem with TED is that people leave the talks thinking they understand more about a topic than they actually do. There's a big difference between having a general sense of the problems a field is dealing with, and actually understanding it well enough to apply it to anything.

I think the first is great when it comes to public understand of science, if you can do it well. The second is a bit problematic when people are left with a misleading impression of what they know.