My server was a Core i7 with 12GBs of RAM, SSD backing and a more or less dedicated NAS. I tried with both SQLite and MySQL backing. MySQL was better, but still unacceptable. If that's not enough to run it for a single user, I can't imagine what it's like trying to deploy it for a full family, even less an organization.
I love the idea behind owncloud, and I admit touting it myself in my own "honeymoon phase", but in hindsight I have no problem admitting that the execution is just too poor.