Thanks Scott. It was broken until sometime in the afternoon. The site would appear to load, but a few items (like one of the new .map files in my original post) would fail to load, and the functionality was broken - eg. if I tried to modify a previously created theme, via the URL in the jquery-custom.css file, it would fail to modify the visual appearance of the theme builder controls.
Anyway, it's come good now, so hopefully it stays that way :)