End users don’t care if downtime is maintenance or error. I think is more honest to show all downtime, not disable checks when you know there will be.
If you have regular downtime, pingdom keeps you honest and might push you towards finding a way to do it without downtime.
It’s not about end-users in my case, it’s about tracking SLA towards our hosting provider. And I agree with you that all downtime should be displayed to end-users, maintenance windows or anything.