I passed on the reports to Dave and he suggested this:
"After the issues over the last couple of days, I would recommend that anybody who is reporting problems holds down the <ctrl> key and refreshes the page. This will flush the browser cache of whatever it *thinks* it knows about the site, which has changed during the diagnosis and fix of recent problems."
The intermittent and inconsistent aspects of our problems suggests to me that this may correct our issues.
Mark