As many of you have reported, there are links that aren't working. This can be cause by 2 different bugs.
If you have an old link and it's taking you to a blank board, or a page-not-found, try those links again. We pushed a code fix for a ton of redirects on old links yesterday. Today, I'm getting a lot of emails and PMs saying that our members' old links are working now! If your old links aren't redirecting yet, let's give it a few more days. These new redirects are cached, and are only cleared once a day. After the cache clears, the redirects render. Most if not all of these should be working next week!
"Unexpected Error" pages
If you click on a link and you get this Error page, this is a page-loading problem related to the Visitor (not verified) bug. The tech team is working on this bug as we speak; it's a top priority. (See my Message Board Fixes - Updates  thread for a full explanation of what causes this.)