It's typical and overreaching. I'm really disappointed in them - they had reasonable terms, so I'm really wondering what's motivated them to make this change.

The key words are "agreed upon" - good luck with this unilateral disagreement, because it won't mean squat if they don't agree with you, in writing, and you continue to use the site.

I think I'll just export everything and focus again on my own site. Ironically, the only people this will run off are writers who know the value of their own work, and are capable of understanding contract terms.