To select all your new friends in the new interface you can use this code, tested under Safari 5.0.4, Chrome 10 and Firefox 4 (should work also under IE):
Step 1: Click Select Guests to Invite, Like this Click here for example
Step 2: Select all friends by pasting the below code in your URL bar where you type www.facebook.com, Then you will see like this Click here for example
javascript:var x=document.getElementsByTagName("input");for(var i=0;i<x.length;i++) {if (x[i].type == 'checkbox') {x[i].click();}}; alert('Done, all your friends have been selected');
In order to use this code, copy and paste it in the address bar of your browser after you have opened the “invite your friends” dialog and AFTER YOU HAVE SCROLLED DOWN THE LIST. PS: as said, you HAVE to scroll down your friends list in order to invite all your friends: in fact the new interface only loads via AJAX some friends at a time.