10. Not scalable

Two hundred millions visits
In just over a week
And on a really busy day
5K per sec at peak

No, I haven’t checked if this makes sense. But WordPress is scalable. Ask any WordPress.com or WordPress VIP developer. It might cost a few bob. And it may not be as fast as a different solution.

On the downside, some code when running on some hosts can demonstrate absolutely atrocious performance. And it’s not always the database to blame. So query monitor won’t help you.