It has happened. We have had exponential growth in mining for sometime as the price of BTC has gone up. As mining is profitable, people add more capacity. But at the size the network is now, adding capacity is actually getting harder. Good cheap 5970, 5870 and 5850 cards are nearly gone. Yes, some of you folks are finding them but you can no longer go on newegg and buy 5 cards. They are not there.
This is not to say that difficulty will not rise, it will. But it is really hard for it to double in one period now, EVEN IF PRICE DOUBLES. I do not know how long this will last, maybe ATI will make more older 58XX chips or the price of the 6990 will drop and there will be a bigger supply. These things are not happening as fast as the price of BTC is rising.
If you have rigs running, you are now in a sweet spot.
There's going to be a dip once we hit the 500k difficulty level.http://blockexplorer.com/q/estimate
Once the dip occurs, I assume BTC prices will drop, then go back up again hopefully to $11 $12.
BTC will become harder and harder to mine, but the cost of the BTC will continue to rise.
Now the only concern for folks like me, 1.2 ghash/s (I can still mine, but I have a better chance of earning more through pools) 2BTC a day @ current is about $20 x 30 days = $600 Mo. USD. Would you wait 20-30 days for 50 coins or $600 per month steady?