Disposing every SPWeb you use... Is it necessary?

I am becoming a bit paranoid about disposing lately. In example.

Until now I would have used things like Web.ParentWeb and then forgotten about them. As I was not "Opening" them manually I was not disposing them either.

Now I usually do things like this:

using (SPWeb web = anotherWeb.ParentWeb)

{

      //Do Whatever you need here with the parent web

 }

I haven't had the time to check whether this is reducing the memory leaks or just making my application more unstable (if I close the web while I am using it somewhere else it could cause an exception it the other part of the code)

Do you think when you dispose a web it automatically disposes every parent web automatically?
It could be...

I need to test this and once I do it I'll post about it.