Warren Buffett just released the latest edition of his annual letter to Berkshire Hathaway's (NYSE: BRK-A) (NYSE: BRK-B) shareholders. Investors all over the world follow Warren Buffett's letters closely, as they aren't just filled with details about Berkshire's operations, but often have some useful investing lessons and wisdom drawn from Buffett's experience.This year's letter was shorter than usual at just 16 pages, but wasn't short on information.