I have a site that was developed in ASP 3.0 and used a lot of include files
to take care of common logic. A common scenario would be an include file
that determined if a visitor was logged in or not and set the users id accordingly.
This user id was then obviously available to every other include file in
the page and all other code.

How do I achieve the same thing in ASP.NET using code behind? I have written
a user control that is included at the top of my aspx page and all the code
will fire on the page_load event. I have declared Public variables in the
control to expose them to other objects and these public variables are assigned
the correct values. What I am not sure about is how do I retrieve these values
from the page that contains the control and other controls on the page?

Any help would be greatly appreciated!