When switching between the different Device Channels you can persist the choice using the DeviceChannel cookie.
When referencing CSS files in HTML files used with Design Manager CSS media queries are removed from the link tag.
SharePoint 2013 introduces the new App Model for deploying customizations. Find out what you need to take into account to convert your existing no-code Sandboxed Solutions to the new Apps for SharePoint.
Mavention Insert Table of Contents is now available as an App for SharePoint.
WCM tip #28: Design Manager: easy start but limiting if you know what you're doing. Build .master yourself
Design Manager allows you to quickly implement your user experience in SharePoint but if you want to build a great public-facing website you should build the Master Page and Page Layouts yourself instead.