I know it's getting popular, though I am still delighted anytime I see a system maintenance page crowded with useful information.
TED is a great example of that: you don't get stuck in their system maintenance page, the other way round!
They are great in suggesting you alternative ways to get to the content you're looking for (at the same time advertising their other channels ;) ) and they explain what disservices could come from the situation and point to a contact email in case of any problem.
Have a look:
Hope to find more and more of these pages around :)
Well done, TED!