Would be even better for newbies if they would also include the Sencha Architect project files .
So I took your advice and I started to port the exemples to Sencha Architect too!
As you cannot import the files to Sencha Architect, I will have to implement them again, so I am going to port the ones that I already have in MVC.
Study the Sencha examples very closely. They are very good.
Here on the foruns there are some users that post examples integrated with other languages (rails, java, php, phyton, .net, etc). These examples can give you a more real feeling of a real app, because you can't have an application implemented with extjs only, you need a server side technology to integrate with.
Learning extjs takes time. Start learning what you are going to use first (most people start learning grids and forms, since they are the most used components on web apps).With time, explore the other components, so you know they exist when you need them. Layouts are also very important.
Learn how to search and use the documentation. The Sencha docs are the best I've ever seen. Most of the times, you will find what you need there.
Read the forum. Don't come here only when you have a question. Read other user's questions and solutions. I've learned so many tricks doing this.
There are several videos on vimeo and youtube about extjs 4. You can also watch them.
Read a book. There a couple of books published about ExtJS (ExtJS 4 First Look and ExtJS in Action). If you are a newbie, I really recommend ExtJS in Action.