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Not sure.

I checked mine and it didn't seem accurate.

Yeah I think there are a few glicthes.

Does that mean the pageviews are not accurate as well?

I am not sure. I have a feeling they might be accurate but I have no way of telling.

The simple analytics will have the pageviews for threads but not posts. I was also thinking, do blog comments and thread replies also count as the post impression?

I would say that threads are thread (threads/posts) related and posts are posts and comments underneath the posts.