Another refactor of a refactor, this time w/o all original comments but w/ proposals. Not currently possible with asynquence, but maybe? *nudge*

async.js

var transform = function(contents, doneTransform) {
	
	var authExpiry = 60 * 60 * 1000,
		authId = uuid.v4(),
		authKey = 'file:auth:' + authId;
	
	redis.client.set(authKey, JSON.stringify({
		userId: req.user.id
	}));
	redis.client.expire(authKey, authExpiry);
	
	// Why no map fn? removes 2 levels of nesting & simplifies the val(fn)
	ASQ().map(contents.files, function(file, done) {
		
		var lookupKey = 'file:path:' + file.path;
		
		// I think it's just as clear to use a callback here... actually, simpler.
		// IMO callback nesting isn't evil, just should be kept in check.
		redis.client.get(lookupKey, function(err, fileId) {
			
			if (err) return done.fail('redis error', err);
			
			if (fileId) {
				fileId = fileId.toString();
			} else {
				fileId = uuid.v4();
				redis.client.set('file:id:' + fileId, JSON.stringify(file));
				redis.client.set(lookupKey, fileId);
			}
			
			file.path = authId + '/' + fileId;
			done(file);
			
		});
		
	})
	.val(function(files) {
		// benefit of map is that you get a files, much clearer
		contents.files = files;
		doneTransform(contents);
	})
	.or(handleError);
	
}