Can somebody explain: what's the harm in getting cracked

Hi,

I was wondering why, apart from bad press, it is a problem if a large website like Linkedin has got millions of passwords hacked, because after all, the user id's that link to the password are not known.

So I'd say: big deal if my password is among the millions being hacked, when you do not know my user id that goes along with it?

What are your thoughts on this?