Most people will not be aware of what is coming up, as they can not access this APUG System Announcements section or simply don't read it, and may be unpleasantly surprised. A pre-warning will help taking care of that.
Maybe you can place a clear message of the upcoming downtime on the APUG's main page, preferably in a yellow box or something to have it noticed easily.
I second brian d's remark: thank you..., you're running one of the most extensive and good community sites out there! Most sites do not advance beyond some basic forum functionality, APUG is so much more than that...