A woman has two kids. One is a boy. What are the odds the other is a boy?

I know.

I read your post wrong. (or rather, hit reply 2 seconds too soon.)

My edit:

But if you aren't given that one of them is heads, then you can't rule out T/T

edit: actually in sicnarf's example, it's still 50% because you are given that the first coin is heads, so you rule out T/T and T/H. So we're left with:

H/T
H/H

Still a different question though.