I talked to a friend last night who was shocked to get a 30-day late notice on his mortgage. It turns out that his loan was sold to a new servicer, and the notice was provided with a regular monthly statement. He doesn't open his statements because he pays his mortgage through his bank's online bill pay service; he just files the unopened envelopes. His last three payments should have gone to the new servicer. The old servicer forwarded two of the payments, but one of them is mysteriously missing.
Now he has to figure out where the missing payment is, make a payment today to avoid another 30-day late, and see if he can GW the new servicer to have the late deleted. This couldn't have happened at a worse time because he was planning to refi his mortgage this month, but now his scores have plummeted and he'll have to wait until (if!) he can get this all resolved.
So - moral of the story - always open your statements! You never know what kind of important notices might be enclosed.