ModernUI is the new style GUI where apps are launched from the new Start screen with Live Tiles, and the apps function in full screen mode and integrate with the new UI elements such as charms and the bottom-flick/right-click menus. It is not just the new Start screen.
R2 can be considered "Release 2". Windows Server 2008 is basically the server version of Vista, while 2008 R2 is the server version of Windows 7.
The Model M is not for the faint of heart. You either like them or hate them.
Gerbils unite! Fold for UnitedGerbilNation, team 2630.