Earlier quoted context omitted.
That LinkedIn not violate one of the simplest, most fundamental notions of security: never ever give your credentials to a third party . Part of being a semi-decent citizen of the internet is also not encouraging users to give third parties their credentials It is a neat hack. I'd love this if it was "here's how we integrate LinkedIn into our email clients internally". It is novel and it does use CSS in weird and new…
To be fair, they specifically mention that they use OAuth for Gmail/GApps. It seems like they're aware of this but it's hardly their responsibility to avoid building a hack such as this just because Google are the only provider to allow IMAP access with OAuth. If more e-mail providers would allow such authentication, I'm sure LinkedIn would be happy to extend the support.
Is that so? "Fsck the world, we got a business to run?"