NO!

It's a JavaScript replacement.

http://en.wikipedia.org/wiki/Google_Dart
http://www.2ality.com/2011/09/google-dart.html

But just like JavaScript it can (potentially) be used for server-side as well (node.js)

Java = Statically, strongly typed language (like C# .NET) with classical inheritance, compile time safety etc.
JavaScript = Dynamically typed language with first class functions with prototypal based inheritance, some runtime safety
Dart = Dynamically typed language with first classes functions, but with some support for static types & classical inheritance, still runtime safety/error checking, no compiling etc.

Dart is more like JavaScript than Java. It's been touted as a JavaScript replacement, not Java. Although, just like JavaScript and Java, it can be used for more than just browser based client-side web apps.

DART is meant to replace JavaScript, not Java. Although it could conceivably be used to write native Android apps, by providing the right libraries and API's, similar to using HTML/JavaScript to build native Windows 8 apps.

Amazon found that a 100ms delay decreased sales by 1%, Google also found similar results where an artificial increase in page loading time decrease the number of searches users performed. So it appears that users DO care, at least at an unconscious level.

Also, you're partly missing the point of faster browsers. As browsers get faster & more advanced, web developers will find interesting ways to take advantage of that extra power and capabilities and deliver more compelling user experiences (look at 3D on the web with WebGL, or ultra low latency two way communication with WebSockets for example). Unless you're one of those Web Luddites who thinks the web should just be black text on the white background with the occasional image.