Why are huge, commercial-like facilities needed for mining when it used to be possible to do it on a laptop?
This means that if only a few people/machines are looking for the next block, like in the old days, then the difficulty is very low.
But when more and more people/machines are trying to find the next block then the protocol raises the difficulty so that even with all these machines trying to find the next block it still takes about 10 minutes to find it.
Right now, worldwide, there are about 6,278,525,000,000,000 attempts to find the next block per second.
Hence it has to be very, very difficult to do in order to assure that it takes on average 10 minutes to find it.
BTW you can see some very intereresting graphs showing all about the current difficulty setting, the next difficulty setting and difficulty history here:
http://bitcoinwisdom.com/bitcoin/difficulty