Did StumbleUpon crash?
It seems that SU is offline for some odd reason. I trust it will recover, but that usually not a good sign.
Check it out: http://www.stumbleupon.com/ (time 10:50AM, PST – Feb 6, 2008)
(update: 10:58AM, PST)
As expected – the site did recover – but here is the screen shot for those that missed it.