I’ve used Google’s Page Speed plug-in for Firebug a lot since it was released last year. Even though it’s not as good as Yahoo’s YSlow plug-in, it’s still very usable for some scenarios YSlow doesn’t support – my favorite being the analysis of unused CSS and selector optimizations.
It also has a feature that will tell you how much your web page will gain by minifying the HTML.
Not only does it analyze the difference but it can also generate an optimized version of your HTML. It removes unnecessary whitespace which in most cases are pretty harmless. But, it does more than that. It actually strips out attribute quotes from the HTML elements as well as remove the closing </body> and </html> tags. This renders the entire page invalid according to any WC3 (X)HTML standards.
Even though it is a good idea to minify your HTML, this feature of the Page Speed plug-in makes it completely useless to me. Unless you’re Google, Twitter or Facebook, this feature is just strange.