On April 12th some technical problems made a few Warcraft servers unavailable. Players with a character in those servers will receive 1 free day of gametime as a compensation. Here is the list of the affected servers:

Affected realms:
Ahn'Qiraj
Bronzebeard
Chromaggus
Dentarg
Drak'thul
Emeriss
Executus
Hakkar
Khadgar
Kul Tiras
Mazrigos
Moonglade
Scarshield Legion
Steamwheedle Cartel
Talnivarr
Trollbane
Vek'nilash
Xavius