I have questions, newbie on board :)

Hi, as tittle of this topic mentioned Im newbie, but I learned read and explored by myself last weeks on bitcoin, cryptcurrencie and markets and anything related to bitcoins mining, ASIC Miners etc !
However, I really got attracted to start mining or trading, I thought to buy ASIC miner, as seems that GPU miners are out of game, but the delays of shipping from Butterfly Labs make me think twice before any pre-order !
I have been monitoring BTC on markets mainly on mtgox.com using bitcoinity.com, and when I started 2 weeks or so, 1BTC ~ 110$, now 1BTC ~ 70$, my question is:
What affects BTC to go down like this, is this going to happend next weeks, is this as some of peeple got their ASIC miners and mining BTC is more faster, and they sell BTC cheaper and cheaper ?

Thanks in advance !