Create a YouTube playlist containing all the uploads of a given user

var credentials = new GDataCredentials(userName, password);
var service = new YouTubeService(applicationName, developerKey) {Credentials = credentials};
var entry = new AtomEntry {Title = {Text = playlistName}};
entry = service.Insert(new Uri(YouTubeQuery.CreatePlaylistsUri(null)), entry);
var id = ((XmlExtension) entry.FindExtension("playlistId", YouTubeNameTable.NSYouTube)).Node.InnerText;
var batchUri = new Uri(string.Format("https://gdata.youtube.com/feeds/api/playlists/{0}/batch", id));
var query = new YouTubeQuery(YouTubeQuery.CreateUserUri(sourceUser)) {StartIndex = 1};
AtomFeed feed;
do
{
    feed = service.Query(query);
    service.Batch(feed, batchUri);
    query.StartIndex += feed.Entries.Count;
} while (query.StartIndex < feed.TotalResults);

Google Data API .NET client library