Our forum is not sending out emails on a timely basis, i.e. sometimes a week goes by before we get a notification of a new post.  We used to get notification messages as soon as the post was submitted.  After upgrading to 4.0.9 they are delayed.  Is this the scheduling service or is there some other settings that can be checked to correct this behavior?

Yes, the scheduler mode is the biggest battle here. If you are using a site with very little traffic, you may want to even consider not using the email queue. Request mode requires that users make additional requests on the site after the scheduled task period elapses in order for the next one to fire off. In timer mode, the next scheduled set of tasks will run as long as they are within the next ~30 minutes of the last period of activity.