The blog was down much of the day while I was busy in Baltimore and Washington (how does it know to die whenever, and almost only whenever, I’m out of town?). Here, according to support, is the cause:
The apache service did not like the initial IPv6 assigned to the domain. I changed out the IP and reset the apache service for the domain and I can now view the domain.
I don’t actually understand how this is possible, but if this is the straight dope, it suggests IPv6 adoption is going to be much rockier than I ever imagined.
Update: I asked for further and better particulars, and got this:
The tech who helped you is not in the office. Therefor I cannot give you an definitive answer. However, I had a similar issue on another machine. It appeared to be a kernel bug. The IP was visible to the VPS guest, but could not use. It appache cannot listen on an IP, it will not start. The best course of action was to simply renumber the IP. Hopefully this gives you more insight. If you have any additional questions, please let us know.
That strikes me as doubtful – craploads of Apache sites are running it natively, including, I think, eight of mine. My tendency is to think that when someone writes “The apache service did not like the IPv6 assigned to the domain” that it’s clearly not ipv6 at fault. That’s not a description of a technical problem, and if something’s dangerous here (and I suspect there is) it’s almost certainly not ipv6.