for a product when we are releasing the product the BA,PM 
will mention what are the new functionalities that we added 
in the current version compared to previous version
what are the open issues and all the higher cader people 
will add all these notes in the release notes
when we install the application the release notes will come 
automatically

In out company we receive release notes when a new build 
(appliction with fixes for the defects raised) is given for 
testing. release notes generally consists of the following,
1. Screens or usecase that are ready for testing.
2. Defects ready for retesting (which are already raised).
3. Major known issues (so that these will not be raised as 
defects).
etc. Release notes help a tester to know what to and what 
not to test.

Correct me if im wrong.

1.In our company we receive the Release notes before the 
release starts.
2.Release notes is prepared and sent by the Developing team.
3.It contains the Defects that are fixed and the 
enhancements that are needed to test for the next release.
4.It specifies the features of that particular release.

release not is prepared by developers , when any new 
functionality is added in the product or bugs are fixed 
which are reported by tester to developer during the 
testing process .This is very useful while testing , we 
concentrate on those parts & we understand which bug is 
fixed and which is left because of priority of bug