Due to the fact the patch is just hitting the US servers and is set to go live on the EU servers later today, the start of the first season of Diablo3ladders.com is postponed 24 hours. This is to ensure nobody gets an unfair advantage by getting a head start. This gives more time for advance sign-ups too. Also, don’t forget that even though a Season has started, you can join the hardcore and softcore ladders at any time.
To take part in the season head to Diablo3ladders.com and if you don’t wish to enter yourself into the season, there is always the Kill Score Ladder or even create your own group to track your group’s progress.