Suppose that I host a project in some open source project hosting services like Google Code, Git hub or Sourceforge, is it a good practice to place the examples / practice code in the repository which I used to learn the technology? For eg., while developing an application I might develop some samples to learn JUnit or Regex and so on. Can I place them in the repository as well? Will it confuse the visitors of my repository?
You should only version what you need to develop/run the project.
Any other set of files could be in its own repository (as a submodule for instance for git), and referenced from the main project if you want.
That way, you still see those file on your main project checkout (if you include submodules), but you can also get your main project without any of those extra files.