My biggest question is what took them so long? If you found Priority Inbox useful on your computer you may find it even more so on your mobile screen.
"If you’ve ever cursed a phone’s tiny screen as utterly inadequate for sifting through an overflowing inbox you’ll be pleased to hear that the Gmail mobile web app now supports Priority Inbox. Priority Inbox helps combat information overload by automatically identifying your important messages so you can focus on those first. Until today it was only available on the desktop and Android devices.
Now, once you set up Priority Inbox in the desktop version of Gmail, you’ll see Priority Inbox sections when you visit gmail.com from your phone’s browser and click on the ‘Menu’ screen. You’ll also see importance markers in your inbox, so you can quickly identify which messages are important."