CSS media queries are great to help adjust the overall styles of a web applications between different devices. With media queries, you can scope the styles based on screen size and have different layouts between desktop and mobile. Tablets like the iPad 3 and various Android devices have large enough screen sizes that it’s hard to scope certain styles to the device outside of the general layout. User agent sniffing is very clunky. Probing the browser for features is the best way to create the best web application user experience for different devices.
What can I do with this?
Does this fully replace media queries?
Does this replace user agent checks?
Mostly. Unless there is a known bug in certain browsers, you can use the browser support coerced with Modernizr to verify and tailor user experience on each device. The only other use for keeping user agent checking would be submitting the information to an analytics system.