Looking at the Web Components overview it doesn't add any addition request unless you build it that way. It basically seems to add HTML templating and a cleaner API for working with events and modifying nodes.
And scoped styles (including only optionally inheriting styles from the parents) and events, which seem like they could be phenomenally helpful for widget libraries. You have to be careful with site-wide CSS to avoid styling, for example, a jQueryUI widget. With this, there would be zero conflicts, unless you explicitly allow them.
