Why is Ruby on Rails so darn slow?
I'm not starting new holy war. And I don't want to force it, but tis is fact. And another cool comment:

Would be keen to know why Ruby-on-Rails is so slow too!
Several of my clients who tried Ruby-on-Rails then abandoned it because of speed and scalabilty. Despite it's other attractions - a big high-traffic website needs something more scalable.
The Python framework Django seems to address these concerns and I have a couple of well-funded dot.com businesses that are using Django for high-profile websites. In fact, due to it's popularity, the main issue is not the technology but finding enough good developers proficient in Django.
ReadyPeople (link)