Static members have a scope of the current worker process only, so it has nothing to do with users, because other requests aren’t necessarily handled by the same worker process.
- In order to share data with a specific user and across requests, use HttpContext.Current.Session.
- In order to share data within a specific request, use HttpContext.Current.Items.
- In order to share data across the entire application, either write a mechanism for that, or configure IIS to work with a single process and write a singleton / use Application.
By the way, the default number of worker processes is 1, so this is why the web is full of people thinking that static members have a scope of the entire application.