I just sweep backwards far enough to catch any old appointments that need to be brought forward. At first, you will find things a ways back, but after a while you won't have to look back more than 1 week.
For sweeping it forward, I look at everything within 4 weeks closely, then just give the next 6 months a quick sweep as a reminder.
Instead of using a monthly calendar view to do this, what I've found helps, is to use a printout of linear calendar view (just a list of appointments printed in date order) to do this. That's quicker. In Ecco you can do a 1-year calendar sweep 60 seconds or less, just by dropping the "Appointments" calendar into a view, then sorting on the date column.
-Steve