I have run into it some times when I had ~100 users online and the screen was just full of error messages. I got 40 mails, some were coplaining and some where explaining what tey did at the moment when I screwed my site up.
Then I really thought that a system to suspend usage for some time would be good idea in the future.
Here we could take advantage of the user system the way that you (as the admin) have everything working (buggy or not) but all the rest visitors get a custom message from admin, no matter where they clik, on the middle saying that currently we do some maintenance , we started some time and shell be done in xx minutes
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