Coursr.us is currently just a website that conglomerates various Google Calendars of coursing and racing organizations and clubs in North America. I wouldn't expect anyone to keep up a full calendar of events for the US or even a large organization, but most secretaries do keep them up for their clubs or area. While we often distribute the work-load, we can still attempt to centralize the data for users.
Why Google Calendars only? Because it's the easiest, free-est thing anyone could ever use. Even if you don't do your scheduling in Google Calendar but use some other calendar program, you can still create a free Google Calendar for your region or club, set its sharing to public, export the iCalendar or CSV from your program and import it into Google Calendar. If you've got that calendar listed here, it will be automatically mirrored to here as well because all this site does it simply pull in other clubs'/organizations' live Google Calendars. In many cases, you can also synchronize a Google Calendar with desktop programs or even with a Yahoo Calendar.
Thanks, and keep in mind this is by no means a complete schedule of every racing or coursing event. You can find complete listings for each organization at their homepages: