There are already alternative sites to Silk Road that have been operating for as long, maybe longer, than Silk Road. SR was just the most publicized/best marketed of the bunch.
BitCoin isn't finite. It is infinite. But "mining" the coins gets harder until advances in technology make it easier.
That is the complete opposite of the truth. There is a total limited number of BitCoins that will ever be mined. That number is 21 million. You are right about the difficulty increasing, but there will never, ever be more than 21 million BitCoins mined.
Read more here.
The dollar value of a BTC dropped slightly where a few panic sold, but really BTC buys so much these days that the argument "It's only for drugs" isn't true - the value will stabilize and rise again soon. In fact now is a good time to buy if you were looking to make a quick buck on a short sale.
Can't you have parts of a bitcoin? Like we have pennies but because they're not real you can have something that costs 0.03333 bitcoins?
The code in the blockchain can be modified by the community to allow a 1BTC to be divided up as many times as they like. Currently I think it's around 8 times, or 0.00000001. Something like that.
Bit Coin wont be going anywhere. Like I said, the whole "It's only to buy drugs" thing was a media spin to effect public opinion. (/tinfoil hat)
BitCoin isn't like fiat currency as the supply is finite and predictable. Fiat can be printed off at any time, without warning.
because they're not real
They're only "not real" in the sense you can't hold them physically. Other than that there is no different to pounds pence dollars etc. I buy plenty of stuff at work that costs 0.004p - I just have to buy a few thousand at a time to make a figure that exists in pounds and pence. With BTC you can pay exactly 0.004 if you needed.