title: Difference between [NSThread detachNewThreadSelector:] and -performSelectorInBackground
body: <p>I've been using <code>-performSelectorInBackground</code> in many of my apps, sort of oblivious to <code>-detachNewThreadSelector</code>.  Now I am wondering what the differences are between the two.  Are they pretty much interchangeable, or are there differences and places where one is superior to the other?  Thanks!</p>