Add note about experimental API

IPython/core/events.py

@@ -7,6 +7,10 b' can be registered for the same event without needing to be aware of one another.'
 
 The functions defined in this module are no-ops indicating the names of available
 events and the arguments which will be passed to them.
+
+.. note::
+
+   This API is experimental in IPython 2.0, and may be revised in future versions.
 """
 from __future__ import print_function
 
@@ -15,6 +19,10 b' class EventManager(object):'
     
     This is attached to :class:`~IPython.core.interactiveshell.InteractiveShell`
     instances as a ``callbacks`` attribute.
+    
+    .. note::
+
+       This API is experimental in IPython 2.0, and may be revised in future versions.
     """
     def __init__(self, shell, available_events):
         """Initialise the :class:`CallbackManager`.

docs/source/config/callbacks.rst

@@ -27,6 +27,10 b' For example::'
         ip.callbacks.register('pre_execute', vw.pre_execute)
         ip.callbacks.register('post_execute', vw.post_execute)
 
+.. note::
+
+   This API is experimental in IPython 2.0, and may be revised in future versions.
+
 .. seealso::
 
    Module :mod:`IPython.core.hooks`