In a follow-up to his earlier SearchEngineWatch article, Gary-Adam Shannon is claiming again that Google may be penalizing sites for using WordPress:
If you ask me, it makes perfect sense that Google could potentially penalize based on a site footprint.
This time he offers two kinds of evidence for this:
 I’ve talked with a few SEOs who also [...]

I was talking to a client the other day about free WordPress themes. I said the safest option is to only use the WordPress.org Free Themes Directory. Why is that?
I talked to her about malicious coding, poor quality coding, out of date coding, etc.
And then I found a very well-researched article by Siobhan McKeown that [...]