Let's pretend I'm a bad guy and ZDnet's unencrypted user database just got uploaded for all to see.

Scenario 1: You use unique passwords on all accounts. It sucks that your ZDnet account is compromised and you'll need to create a new password, but the pain ends there.

Scenario 2: You use the same password on ZDnet as you do elsewhere. I take the credentials from ZDnet and start trying to log into PayPal, Newegg, Facebook, iCloud, Yahoo/Gmail/Hotmail and various major banks. That might take a bit more effort to clean up.

http://www.computerworld.com/s/article/9217646/LulzSec_s_Sony_hack_shows_rampant_password_re_use highlights the dangers in password reuse.