The best rebuttal I've seen to the case that the credit crunch isn't all it's cracked up to be comes from David Beckworth. He looks at the money multiplier for the monetary base. The idea behind the multiplier is that the Fed increases the base by lending money to banks. These banks keep a fraction of the money in reserves, as determined by the Fed, and lend out the rest to others. The borrowers then spend the money which eventually winds up being deposited at other banks, where the process begins again until there is no money left to lend out. The amount of money created in the entire economy because of the intial injection from the Fed is multiplier.
But if there is a credit crunch, then even as the monetary base expands because of the Fed, the money supply does not because banks aren't lending. I'll give it over to Beckworth from here:
One implication is that if, in fact, there is a credit crunch then the money multiplier should be sharply falling. Thus, it makes sense to look at the money multiplier. The figure below provides the money multiplier using MZM as the broad measure of money and the St. Louis Fed's monetary base measure. (See here for why MZM is used over M1 or M2.) The data are on a bi-weekly basis and go through the week of 10/8/08.
These figures may not settle the debate, but they do suggest that we are closer to a systemic credit crunch than to a minor credit market hiccup.