The song is "Tell Your World" by KZ Livetune.
They also used other popular person such as Justin Bieber and Lady Gaga. The theme is how these person (well, I think Hatsune Miku can be a person too?) change the world or themselves by using the internet, or to be precise, Google products like Chrome, Map, Gmail, Google+ and Youtube.
The last advertisement, I think is about a father who post videos, pictures and blogs of his daughter on the internet, to show how much he love his daughter. Kinda heartwarming.
Overall, Hatsune Miku wins over Bieber and Gaga.