What methods do people use to notify users of upcoming downtime in an application, and for handling requests nicely while scheduled downtime is occurring? My Google-fu is not yielding me anything useful-looking.
Depends, the easiest way is to use capistrano: http://www.google.be/search?q=capistrano+maintenance+page
It will put a maintenance page in the public folder for the time that your app is offline.
There’s other ways to do it, like handling it in Apache itself if you’re using Mongrel cluster, like checking if the mongrels are up and if they’re not, serve a custom error page.
Best regards
Peter De Berdt
And concerning the notification, it’s all up to what you personally prefer tbh. One way to go about it is create a Downtime model and with a start and end time, put a before_filter in application_controller.rb that fetches all those > Time.now, then show them by rendering a partial into every view if the number of records is higher than one.
Best regards
Peter De Berdt
What methods do people use to notify users of upcoming downtime in an application,
We use comatose to manually post a very visible notice about any scheduled maintenance...
and for handling requests nicely while scheduled downtime is occurring?
... though we have 2 load-balanced servers, so generally we can get
away with updating stuff invisibly 
I was contemplating methods of easily having a pop-up or banner to say "the site is going down in ten minutes". That sounds like a nice reusable one.