Many folks this afternoon playing on EU servers have tipped us to the issues going on with Battle.net. It seems that they are unable to logon, with all accounts being stuck on the "Connecting" phase.
This is really bad timing for this to be happening, as it was just announced yesterday that on November 11th in the US and November 12th in the EU all accounts will have to be converted to Battle.net accounts. Many people are concerned that these problems will persist through the conversion, although it's important to remember that these issues have existed before Battle.net came about as well.
There has not been any official word from Blizzard on today's EU problems, but that hopefully be coming along shortly -- along with an idea of when it all will be fixed.