In 2010 I set up this blog on Tumblr mostly due to the ease of publishing and not having to worry about the hosting. I also went through…
From my experience, PunyPNG produces better results than Smush.it does.
The sprite image for this blog yields 160kb when it was created. Smush.it reduced the size by 30%, PunyPNG reduced the size by 50%.
The PunyPNG API is going to be extremely useful when it is out of beta.