The good news is that it may explain some of the errors we've been having before this occurred; as I was unable to find another explanation for it.
Unfortunately it sounds like my hosting provider is keen to move servers away from the cluster that suffered this failure, which means there will need to be more downtime in future; this will be scheduled so I'll be able to give advanced warning of it, but I'm not sure how long something like that will take, probably at least a full day's downtime, if not more if the IP address changes.
On the plus-side; the downtime was 100% not my fault

Update: Okay, definitely take instability as a given; it seems connections to the site are a bit hit and miss at the moment. It's a little better than it was earlier, so hopefully will improve throughout the day!
Update 2: It looks like load on the server has decreased and things seem to be running pretty smoothly; I'd still recommend caution/low expectations when posting or uploading something huge, but hopefully we're back to normal!