Novelists: do you have a specific person (an Ideal Reader) in mind when you write?

“I like to tell my writers to write for their mentor or fiercest critic. Write to the top of your form”—Betty Lerner, Forest for the Trees

Stephen King also mentions the Ideal Reader (his being his wife, Tabitha) in his book On Writing.

I know that some of my best writing actually takes place when I write letters (I’m still one of those people who persist in writing snail mail). When I have a clear audience in mind, my writing becomes much more focused than, for example, in my journaling. The necessity of communicating bulldozes through any attempts to sound pretty or fancy. In fact, a lot of my blog entries originated from letters to one friend or another.

But when it comes from writing novels, I don’t seem to have a particular, specific audience in mind. (I’m wondering if that is a reason that I’m having so much trouble?) .. so, fluther novelists—do you write with someone in mind? How does it work (or not) for you?