I'm not exactly sure because I sold my first WoW account, but:
WoW - easily 10,000 hours
SC2: Not sure, but 11,472 career games
D3 - 1,800 hours.
LoL - Maybe 1,000 hours(300 wins).
I think I'll just stop thinking about it there.
EDITED: updated to be more accurate after reviewing some info.