Finding Your Voice. Who is Your Audience?

So I decided to start another blog to talk just about web writing. I'm all excited and I send the link to a friend and she asks me this question that has stopped me in my tracks:
"Who is your audience?"
Okay, are your ready for irony? One of my first posts is about Writing with The Reader in Mind.
And yet I haven't defined my blog audience.
Do you have a blog? Have you identified who your audience is, or at least who you'd LIKE it to be? Or do you just write into a vacuum and figure someone out there will find you and make a connection to what you have to say?
In your corporate communications – internal and external – it is critical to understand your audience; what motivates them, their level of understanding, etc.
Is it important with a blog?
What do you think?
Deborah Chaddock Brown
Professional Writer, Ponderer of Audience Members
AllWrite Ink