Not often.
I usually read the popup describing the first lines of the thread and decide if I think it's interesting from there.
I try not to know whose posts I'm reading as I read all the posts in a thread, too.
That way, if somebody has written something particularly good or bad, I arrive at that conclusion sans whatever prejudice I might already have about that author.
Sometimes people who I generally think are pretty dumb make some fairly acute observations or comments.
The point is one never knows where one might find a new perspective or factoid, and if you come to it not knowing who has written it, you'll evaluate it more honestly than if you read it knowing its author.
In a place like this, it's what is written on the page that really matters, not how you or I might feel about the personality that wrote it.