Yep, Natal will be available in Cydia. It will also be a paid release, just so people know. But, apart from just the icons found in here, many if not all will see atleast minor improvements, some massive. Plus other things like notification center, switcher controls, sbsettings, alerts, dock..etc, lots of UI goodness basically. I will ofcourse continue to support it by adding to it all the time, taking requests and templates will be available for user's to make icons of their own.
First you will need a jailbroken iphone4/s with Winterboard installed from cydia (winterboard is the app that applys the theme). To get the theme from your computer to your device you can use iFunbox (freeware). When using iFunbox navigate on your device to Root > Var > Stash > Themes. Then drag and drop the folder of the theme you downloaded 'May - Retina' and drop it into the themes folder you just found. Now just open up winterboard on your device and tick May - Retina in your list of themes and respring to apply.