"In short: what defines the novel as lesbian, the fact that the author is lesbian or the plot?"
This is a very interesting article. I enjoyed Tipping the Velvet and I adore Jeanette Winterson. The fact that some of her novels have lesbian characters didn't determine nor define my appreciation.
And I figured if I am too sick to write my own thoughts I'd just share someone else's until I feel better. Any day now . . .