Anybody remembers when did the steam summer sale started last year?

Well a quick google says July 11

11-22 July http://store.steampowered.com/news/11069/

Not soon enough

2nd week of July, but the "mysterious" cards are dropping now, so the sale is imminent.

winter sale special cards were available December 10th, winter sale started December 19th. Summer cards showed up today, so I expect the summer sale to be on the 19th. If there are no weekly deals on Monday next week, we'll know for sure.