Ask HN: Does Google punish sites?

I own a website for rental applications. I've been in PR2 for my target keywords for a year or so now.

I recently hired a SEO consultant to try to get my into PR1. And BAM! My site is suddenly PR12, my visitor rate has plummeted, and even my Adword ads seem to get pushed to the bottom.

I wanted to know if the HN community has any experience with this. I've done a bunch of research and gotten mixed opinions. Would appreciate some feedback.