There are many alternatives which you can use instead. Thes include JQuery & JQueryUI, YUI, Sencha (ExtJS) and Dojo.
The library also gives a testing framework which is similar to other test frameworks like QUnit, mocha or jasmine.
The Closure Linter checks your code style to make sure it is always readable by other people in your group.
Linters are well known for hurting people's feelings - so be sure to run them often, you can even get JSHint as a plugin for Textmate.
The latest recent addition to the closure toolset is Closure Stylesheets. This allows you to to write CSS in a more programmatical way. One of the large benefits with Closure stylesheets is the minification and class renaming which can save even more bytes.
Alternatives are LESS and SASS and compass. You may still want a CSS minifier to use afterwards and you can use Yahoo's
So it's a pretty complete set of tools - the only thing that is really missing is a way to structure your code (and perhaps an IDE). Next blog article I'm going to take you through creating a local application which will be followed by posts about building and serving your application on a server. In those I will introduce you to Plovr and talk about creating a node proxy script so you can test pages "live".
I'd also recommend you pick up the Closure Definitive Guide, which you can also get on Amazon for your kindle.