Is Boo a real useful language into unity3d or is just keep as backward compatibility?
I found that even some samples and manual show information in c# and in javascript but Boo.
Boo as far as I understand is based heavily on Python. As such, it should be a good starting language for those that aren’t very familiar with programming. I’m fairly certain that you can do anything you want in any of the three languages however. You just may have to go about it in slightly different ways.
As with JS and C#, Boo has complete access to the unity API, and as with C# (probably also JS but I’m not sure) Boo has complete access to the Mono runtime.
It is kinda’ a bummer that all documentation examples are written in JS, a few in C# and none(?) in Boo, but it’s not that hard to get examples working in Boo. The trickiest for me was co-routine syntax, but a quick search of the forums helped me out. 
Oh, and as far as versions go Unity does ship with an earlier version of Boo, but I found that if you install the most recent version of Boo, Unity will use it.
Boo?
…sorry, I’m no help.
Boo is amazing, who doesn’t want to use it? All the examples and tutorials should easily port to Boo. If you add a new Boo file in a Unity project, and can get you started with basic syntax, and the Unity code is just the same. Pretty easy, just gotta know Boo.
There is a online converter, that can do C# to Boo conversion, nice to compare code
http://codeconverter.sharpdevelop.net/SnippetConverter.aspx
Hehe, that would support the idea of getting more examples etc. written in C# - since that would mean they would immediately be available for Boo, too.
And I think writing a conversion from C# to UnityScript/JavaScript should be possible, too. Any volunteers? 
Good find! Thats going to come in handy for plenty of people.