Thoughts on Smush.it
I developed a plugin last year that integrated Stoyan Stefanov and Nicole Sullivan’s Smush.it service with WordPress. In a nutshell, it reduced the file size of all images uploaded to WordPress without losing any quality.
Stoyan and Nicole are Yahoo! employees, and Smush.it was moved under the Yahoo! banner fairly soon after its launch. I was pleased to see that move. Long before Google-hosted jQuery and Closure, Yahoo! was making high-quality tools available to web developers (YUI library, YUI Compressor) for free. They integrated Smush.it with YSlow and put up a basic web interface.
Since then, Yahoo! has moved Smush.it fairly often, and I’ve been playing cat-and-mouse with them, changing the API endpoint URL in my plugin to try to match their changes. This has been in response to a bunch of support requests from my users in the forums, and many more by email.