One space or two

I just came to realise there is actually some sort of debate whether there should be one space after a fullstop, or 2 spaces.

I am not sure. What do you think?
I am not sure. What do you think?

I always use one. I never have a problem with that.
I always use one. I never have a problem with that.

Is it quite obvious that I'd just went mad?

Postnote:
Forget it. Blogger will autocorrect it to be one space after full stop.