Thoughts on YSlow Feedback
If your using multiple web servers then ETags need to be configured correctly. Add this to your .htaccess file (at the bottom) if this is the case. If you only have 1 server then you can safely ignore this recommendation. 

FileETag MTime Size


Cookie-free domains offer a slight performance improvement because less data will be traveling over the wire. You need a CDN to get a cookie-free domain setup correctly.