Here's why people are so angry:

* they clearly didn't hear about it in advance

* it was buried in the midst of discussing (minor) new features

* it locked them out of features they had before (XML export)

* it's a 2-3x increase for many people

* the grandfathering option forces them to come up with thousands on short notice, or not at all

* ZenDesk's blog managed to sound totally smug

* nobody from ZenDesk is answering emails, phones, or even comments

Basically, it's a nuclear disaster.

EDIT: Fixed line break issue. I never remember...