This code is in a UITableViewController subclass viewDidLoad method. The UITableViewController subclass contains a test method.
It crashes without throwing an exception.
id dict = [[NSMutableDictionary alloc] initWithObjectsAndKeys: @"some text", @"text", @selector(test), @"selector", nil]
pix0r's solution is good, but I usually prefer to use strings because they're more resilient to serialization and make the dictionary easier to read in debug output.
// Set selector
SEL inSelector = @selector(something:);
NSString *selectorAsString = NSStringFromSelector(inSelector);
id dict = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"some text", @"text", selectorAsString, @"selector", nil];
// Retrieve selector
SEL outSelector = NSSelectorFromString([dict objectForKey:@"selector"]);