Dynamic blocks and left sidebar not behaving as expected

I've been trying, for a few weeks, to get the left sidebar to work in a more dynamic way - but I've failed to make it work. I've been using CCK and a computed field in order to create nodes that store a value under the $_SESSION variable - and then created blocks to the left sidebar that should behave based onthe $_SESSION variable.

Basically my node's computed field would be something like:

$_SESSION['current_customer']="Google";

And my left sidebar block would carry a conditional statement:

if ( $_SESSION['current_customer'] == "Google" )
    return TRUE;
return FALSE;

I would then have nodes for Google, Yahoo, and other sites.

The nodes are triger or invoked using the "Primary Links" menu. I've noticed that when I create/edit and save the node, the left sidebar block will show the block for the corresponding $_SESSION['current_customer'], but if I click directly on the Primary Links the blocks don't react. I placed some debugging code and see that my $_SESSION variable is indeed changing as I click on my other links, but the block does not appear to do react to it. Is there a trick that I am missing?

Here is a quick view to the issue:

http://www.flickr.com/photos/22121475@N04/2132654055/?addedcomment=1#preview