As I heard the Bitcoin bubble started around April 2011 due to an article on Bitcoin in some news website. What article started the Bitcoin bubble?
Press inquiries to me really picked up after the Forbes article came out in the print edition of that magazine. I think that "mainstream press" mention started the publicity avalanche that fueled the bubble, although I'm a pattern-matching monkey like everybody else so take my opinion with a big grain of salt.
There were events that coincided with Bitcoin's rapid ascent, but not necessarily does that mean those events caused the bubble.
Jason Calacanis' "Most dangerous open source project ever" post was one such time where the price spiked at the same time.
Jerry Brito's article raised some good attention and subsequent coverage in Forbes didn't hurt either.
The real catalyst that got things started in Spring 2011 though was February's Security Now podcast with Steve Gibson.
they started spamming Bitcoin-threads on 4chan's technology board. then the bitcoin prices started to rise. after the spike no one ever mentioned bitcoins again on 4chan. /job done/
personally i think they reached currency speculators through 4chan (they also talk about finance, financing options and how much money they make through trading) and as a currency speculator, you know the weak spots of money.
I thought it was "Underground Website Lets You Buy Any Drug Imaginable" in wired.com's "Threat Level" on June 1, 2011 that triggered the bubble. The bubble really started just after that date.
A Slashdotting of BitcoinJ is the first time that I personally saw Bitcoin mentioned anywhere ... and with a Google Engineer behind it.
This was a big one that probably didnt start it, but fueled it and kept it going, http://falkvinge.net/2011/05/29/why-im-putting-all-my-savings-into-bitcoin/