See http://clang.llvm.org/docs/ObjectiveCLiterals.html for more information, but some examples from that page:

  NSNumber *fortyTwo = @42;             // equivalent to [NSNumber numberWithInt:42]
  NSNumber *piDouble = @3.1415926535;   // equivalent to [NSNumber numberWithDouble:3.1415926535]
  NSNumber *yesNumber = @YES;           // equivalent to [NSNumber numberWithBool:YES]
  NSArray *array = @[ @"Hello", NSApp, [NSNumber numberWithInt:42] ];
  NSDictionary *dictionary = @{
      @"name" : NSUserName(),
      @"date" : [NSDate date],
      @"processInfo" : [NSProcessInfo processInfo]
  };

This, especially the NSArray/NSDictionary stuff, should make coding in Obj-C so much faster and more pleasant - well done LLVM team!

PS: Not sure if the object subscripting stuff is supported yet, but that looks awesome too!