Yes, even if you send a high quality PNG image to facebook, they will convert it to a low quality JPG.  This is especially bad for things with text.  See: <a href="http:&#x2F;&#x2F;lbrandy.com&#x2F;blog&#x2F;2008&#x2F;10&#x2F;my-first-and-last-webcomic&#x2F;" rel="nofollow">http:&#x2F;&#x2F;lbrandy.com&#x2F;blog&#x2F;2008&#x2F;10&#x2F;my-first-and-last-webcomic&#x2F;</a>