Several third party sites provide that information.

http://boincprojectstatus.ath.cx/

And, the 78.23% rating presently there is hilarious. no one at all has been on the boards to report inaccessibility of the work distributors.

If there is no work: This is signaled in the message log. That's why there is the "if there is no work for.... give me something else" option to keep clients busy.

Their credibility was much higher on the % front, when they sampled more frequent, which they now do not.... The sample is from 50 minutes ago, where actual is noted from own test:

Results as of 07/08/2008 08:14:15 GMT.

Scheduler is up - correct
All download servers are down. You will be unable to fetch work. - incorrect
Upload handler is down. You may be unable to upload results. - incorrect

Other sites give only a colour indicator like this:


Point though of these sites is, that if you have a problem, you go there to check. You don't go there if you don't have a problem. I don't, but when the message log says there might be one.

If they are, then they're doing it wrong - the WCG scheduler runs continuously through the stats update.

Scheduled downtime is usually for a couple of hours on Sunday. That's the normal maintenance window, anyway - it is only used occasionally.

I can't remember when the last unscheduled downtime was. 6 hours in May, according to Known Issues.