I am learning hibernate is it useful ?

I never liked ORMs. Preferred direct SQL interactions

Nevertheless, demand for Hibernate and such from the market has never decreased

Depends. Its useful as a JPA provider. The Criteria API should be avoided.

Yes, it's arguably the most used persistence API for Java (and it's not a bad one either.)

If you want to do server side Java work, Spring + Hibernate are pretty much essential to know.

No the human body isnt build for it. At the end of the hibernation period you will be dead unless you are under care by others like people in a coma.

@irene great, then I can use it in the summer :)

@irene the device that keeps you alive while in a coma

I've seen it commonly used for Java BEs.
The adequate twin sister for C# is NTT Framework.

Depends. It's sometimes regarded as a trap because it's not as simple as sql to create an application with optimal performance. It is slightly more difficult than JDBC and offers no new functionality to the application. In theory when you know how to use it properly you can spare some development time (and thus money). In reality it's often a trap so consider it with some caution.

@beggarboy this is the first time I see someone using NTT for the entity framework.. I use it regularly but had to quack it to see what NTT was xD