The code for MusicGrabber, which can save music from iPod-library to your Documents or Caches.

MusicGrabber.m

+ (void)saveMusicFromURL: (NSURL *)sourceURL
                  toFile: (NSURL *)destURL
              completion: (void(^)(BOOL success))_completion
{
  AVURLAsset *asset = [AVURLAsset URLAssetWithURL:sourceURL options:nil];
	
	NSError *err = nil;
	AVAssetReader *reader = [[AVAssetReader assetReaderWithAsset: asset
														   error: &err] retain];
	if(err)
	{
		[reader release];
        _completion(NO);
		return;
	}
	
	AVAssetReaderOutput *output = [[AVAssetReaderAudioMixOutput assetReaderAudioMixOutputWithAudioTracks: asset.tracks
                                                                                           audioSettings: nil] retain];
	if(![reader canAddOutput:output])
	{
		[reader release];
		[output release];
		_completion(NO);
		return;
	}
	
	[reader addOutput:output];
	
	AVAssetWriter *writer = [[AVAssetWriter assetWriterWithURL: destURL
													  fileType: AVFileTypeCoreAudioFormat
														 error: &err] retain];
	if(err)
	{
		[reader release];
		[output release];
		[writer release];
		_completion(NO);
		return;
	}
	
	AudioChannelLayout channelLayout;
	memset(&channelLayout, 0, sizeof(AudioChannelLayout));
	channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
	NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
									[NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
									[NSNumber numberWithFloat:44100.0], AVSampleRateKey,
									[NSNumber numberWithInt:2], AVNumberOfChannelsKey,
									[NSData dataWithBytes:&channelLayout length:sizeof(AudioChannelLayout)], AVChannelLayoutKey,
									[NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,
									[NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,
									[NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,
									[NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,
									nil];
	
	AVAssetWriterInput *input = [[AVAssetWriterInput assetWriterInputWithMediaType: AVMediaTypeAudio
																	outputSettings: outputSettings] retain];
	if(![writer canAddInput:input])
	{
		[reader release];
		[output release];
		[writer release];
		[input release];
		_completion(NO);
		return;
	}
	[writer addInput:input];
    input.expectsMediaDataInRealTime = NO;
	
	[writer startWriting];
	[reader startReading];
	
	
	AVAssetTrack *soundtrack = [asset.tracks objectAtIndex:0];
	CMTime startTime = CMTimeMake (0, soundtrack.naturalTimeScale);
	[writer startSessionAtSourceTime: startTime];
	
	__block UInt64 convertedByteCount = 0;
	
	dispatch_queue_t mediaInputQueue = dispatch_queue_create("mediaInputQueue", NULL);
	[input requestMediaDataWhenReadyOnQueue: mediaInputQueue
								 usingBlock: ^
	 {
		 while (input.readyForMoreMediaData)
		 {
			 CMSampleBufferRef nextBuffer = [output copyNextSampleBuffer];
			 if(nextBuffer)
			 {
				 [input appendSampleBuffer: nextBuffer];
				 convertedByteCount += CMSampleBufferGetTotalSampleSize (nextBuffer);
				 CFRelease(nextBuffer);
			 }
			 else
			 {
				 [input markAsFinished];
				 [writer finishWriting];
				 [reader cancelReading];
                 
                 
                 dispatch_async(dispatch_get_main_queue(), ^{
                     _completion(YES);
                 });
                 
				 
				 break;
			 }
		 }
	 }];
	
	[reader release];
	[output release];
	[writer release];
	[input release];
	
	return;
}

Do not forget to import AVFounddation

SourceURL is maybe next:

NSArray *items = [mediaItemCollection items];
MPMediaItem *_track = items[i];
NSURL *sourceURL = [_track valueForProperty:MPMediaItemPropertyAssetURL];

Dos you have any experience if this "grabbing" is according to the Apple guidelines or will this be rejected during the compliance test?