After a regular search, I noticed an SU icon next to every single search result (odd). Clicking on it, I was met with the following (click for fullsize):

Good stuff - they are down, and they will be back up at 8pm.

But wait - 8pm where?

It was plausible that StumbleUpon is doing some IP tracing, figuring out where I live, and then being super-friendly and letting me know that it will be at 8pm. Unlikely, but maybe. A quick check with a friend in the Far East yielded the same message - 8pm.

Thanks guys, but that message is almost as useless as ‘back soon.’