Amen to all of the above, Jeff. If it were just lots and lots of traffic, the average user should be able to deal one way or another–I, for one, got plenty of practice with that back when the bandwidth limits were a lot lower at DreamHost.
It’s just that nagging fear of saying “hey, this file’d be cool to put up”, then waking up one morning to find a DreamHost “your bandwidth is projected to be 800GB this billing period” message in my inbox.
No amount of preperation or tweaking can perfectly protect from sudden, exponential popularity, which is why it’d be nice to have some way to just say “if this subdomain/file/directory exceeds 5GB in a month, 503 it and let me know.” Maybe someday that feature’ll be announced in the newsletter.
On the other hand, if I had any time/talent I could write a script to spit out file x and keep a count of the number of times that happened, then stop spitting it out when the counter reached some number. Not foolproof, I suppose, but better than nothing.