Apparently there was some extra downtime (7 hours!) for some of the European realms on Wednseday. To compensate, Blizzard is giving a one-day playtime credit to anyone with an active character in the affected battlegroups: Crueldad, Hinterhalt, Némésis, and Nightfall. That's one of the things I like about Blizz -- they may mess up, but when they do, they try to fix it (except when it comes to Life Tap).
In case you're not sure what battlegroup you're in, here's the realm listings. If you have an active character on any of these European realms, you will be credited a day of playtime.
- Crueldad: C'Thun, Dun Modr, Los Errantes, Minahonda, Shen'dralar, Tyrande, Uldum, Zul'Jin
- Hinterhalt: Arygos, Der Mithrilorden, Dethecus, Forscherliga, Norgannon, Teldrassil, Todeswache, Un'Goro
- Némésis: Arak-arahm, Confrérie du Thorium, Eitrigg, Garona, La Croisade écarlate, Medivh, Uldaman, Vol'jin
- Nightfall: Alonsus, Anachronos, Bronze Dragonflight, Burning Steppes, Darkmoon Faire
Darkspear, Kor'gall, Lightbringer, Molten Core