[support] Cookies and SSL

[Don]

I've recently updated to the latest version of Drupal 6, and I'm having 
a terrible time with session info getting lost when switching to ssl for 
checkout.
I have set $cookie_domain to .example.com and $base_url to 
http://www.example.com.
when I go to checkout at http, I have a full cart. When I go to checkout 
at https, I have an empty cart. It just looks like the cookies looked 
for are different.

In both cases, the only difference in the url is 'http' and 'https', 
there's no domain change.

is there anything else I can check for?

thanks.
-Don-