I installed Fooman Speedster today (I've used it before without problems) and set it up as per the guidelines. I didn't experience any of the common issues however when loading the page I noticed all the JS was unavailable. I viewed the source to see a correctly generated minified link for the JS files, however on clicking it and attempting to view the result I get a 403.
As regards the CSS, this minifies and displays perfectly, and doesn't return a 403 when trying to view. I've been through the troubleshooting, checked permissions and there are no obvious faults, I just find it odd why the CSS works and the JS doesn't? Self tests passed without a problem and all relevant .htaccess files are in place.