HUH?
Get a new ISP.
The only way you'd be having issues is if the board switched to a new host in which case 24-48 hours all the issues would be cleared up. Of course, Most folks running web sites set up the redirect on the old site so nobody notices down time (no matter which domain you type in, the old would redirect to the new IP).
More likely the issue is one of the major players having problems with their service, Quest was always bothersome in the past in dropping traffic.
Anyway, the guy should of known better, and might have a filter problem on his end (site block).
Try this to see if it's a nameserver issue - on you machine open start > type cmd and hit enter
In the black box that comes up type ping
www.jim-butcher.comsee if it does anything
Then type
ping 69.89.31.150
and see if that's different
if it is, Try opening your browser and using
http://69.89.31.150/ and see if that gets you to the site.
hope that helps.
edit - no, that ip won't get you there, and I could be wrong about the server settings.
On a side note, something that could help performance problems would be to go to crystaltech.com and host there.
I use it for my site, I'm on the 36.95 premium package.