For the past week I have been watching a drupal site bounce off the rim of total disaster. It's a great site, new content every day, and the future is bright, but it simply has WAY TOO MUCH PHP.
One thousand php notices and warnings per minute. One hundred and fifty users with administrator access. Five hundred twelve megabytes of memory required per php thread. Typical page loading times of 6-10 seconds. Frequent gateway errors, weekly disasters.
I like a Drupal a lot. It's the fastest way to make a complex website, and if you do it right, it's quite scalable.
On the other hand, Drupal also seems to be the preferred tool to make the worst websites on the internet. If someone could create a service to sort out these sites it would have many clients. There is a great trove of content trapped in these crippled applications.