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Summary: NSDateFormatter's default date has changed to be 1/1/2000 in iOS 6, rather than 1/1/1970 in iOS 5 and earlier.

Steps to Reproduce:

Create an NSDateFormatter
Set a date format containing just a time formatting component
Create a new date from a string providing time information only
On iOS 6, the new date will use your supplied time, but the date will be 1/1/2000, rather than 1/1/1970

A sample project is attached. Run this project, and note the following code in viewDidLoad: in ViewController.m…

	NSDateFormatter * timeFormatter = [[NSDateFormatter alloc] init];
	[timeFormatter setDateFormat: @"HH:mmZ"];
	NSDate * date = [timeFormatter dateFromString:@"12:00 +0000"];
	NSLog(@"Date is %@", date);

on iOS 5.1, the output will be a date of 1970-01-01 12:00:00 +0000.
on iOS 6.0, the output will be a date of 2000-01-01 12:00:00 +0000.

Expected Results:
On iOS 5 and earlier, the date part of the new would be 1/1/1970, i.e. the Unix epoch; I would expect consistent behaviour on iOS 6.

Actual Results:
On iOS 6 and later, the date is 1/1/2000. Note that this is neither 1/1/2001 (the reference date) nor 1/1/1970 (the UNIX epoch and previous default date). This causes inconsistencies in date maths between dates and times created on iOS 6 and dates and times created on iOS 5 or earlier.
Note also that the new default date of 1/1/2000 appears even if apps are compiled against versions of the iOS SDK earlier than iOS 6. We are seeing this behaviour in an app that was linked against iOS 4.2.1, for example.

Regression:
iOS 5.