Json.NET should be used serialization and deserialization. Provides serialization and deserialization functionality for AJAX-enabled applications.
Is it deprecated
No or else they would of marked it as Obsolete
should this class not be used in general
I can't see any reason not to use it if you want to. So feel free to use it, but read the below first:
It seems Microsoft can't make up their minds about making it actually obsolete. My guess is they still maintain it because it's used internally and re-writing stuff to use Json.Net is just more work than it's worth.