I find myself saying hmmmm quite a lot.
it's quite useful.
Preferable to saying something like 'what a @@££$$%%^^ ing stupid idea', but it's a bit of a cop out.
It does imply that I am thinking about what you said, when in reality I probably don't care.

So if I write Hmmm in one of my blogs or my comments, I give you permission to write something rude back to me.

That fair enough?

OK, well, let's give that a try shall we?

Ready?

Hmmmmm ....