I've just finished putting together a progress display page for a couple of long-running operations in our application, and I think a similar approach could work for you.
We do a bunch of server-side image processing in some situations, which can take quite a while. The page that gets submitted to forks off a background thread with ns_thread begindetached and then redirects to a progress page that refreshes itself every 30 seconds. The background thread communicates with the progress page through an nsv that's keyed by task_id, updating several progress stats, and the progress page tells the user where the process is up to. When the process is finished the progress page sees this in the nsv structure and presents a "continue" link to the next step in the process.
ideally, I'd like to generalise this to a dropin replacement for the "waiting" page used by the package installer...
