Yes, extremely bad.

Email sales rely on the fact that people need to take action to get the email out of their face. It's an attention-intensive process.

This will shift that dynamic to the other side, where people will need to go out of the way to check their marketing messages. For sites like LivingSocial, it'll be especially bad because those deals may expire before they're even seen.

Doubtful. I think people who enable things in their gmail labs are probably already filtering out the mail from marketing campaigns they don't care about.

It will be interesting how this affects my open rate for Hacker Newsletter. I'll write something up and share if it does.