I don't know if this has been suggested yet, and I haven't finished doing the upgrade to check if it's already there, but....

How about an On/Off button in the Admin section to put a "Temporarily Unavailable" page up?

Sometimes our users get out of hand, or our server goes nuts, and the rest of our team relies on my limited knowledge to handle the website, but I'm on the road a lot. It would be much easier to give them an On/Off button. And it would be easier for me when doing upgrades and such.

Cecilia :-)