Who'd have thunk it? They have a "be right back" message posted, saying the site would be back online by 5:30 PDT August 8, 2008 (that's like 30 minutes from right now). Here's the message...
LinkedIn Will Be Back Soon
LinkedIn is currently unavailable while we make upgrades to improve our service to you. We’ll return around 5:30pm (PT) August 8th, 2008.
We apologize for the inconvenience and appreciate your patience. Thank you for using LinkedIn!