The more money they create, the more the Bank of England's policy makers must wish they had better things to spend it on than government debt.
Of the extra £175bn the Bank has created through its QE policy since March, around £173bn has been used to buy UK gilts. That's no great surprise. But it is far from ideal.
When the policy started, the chancellor authorised the Bank to buy £150bn worth of assets, of which "up to £50bn" could be private sector debt.
It's fair to say that limit has not been reached: as of now, the Bank's Asset Purchase Facility (APF) has spent just £2bn on commercial paper and corporate bonds.
Why buy mainly gilts? The justification was three-fold. First, by boosting demand for government bonds, you lower the interest rate on that debt, and since that (risk-free) rate sets the floor for rates across the board, you should lower the cost of borrowing for firms and households as well.
Second, by buying only risk-free public debt you prevented the Bank from taking a lot of private sector risk onto its balance sheet (a particular concern earlier in the year when there was so much uncertainty about what all that securitized private debt was worth).
But the final, and most telling, reason was that there simply wasn't enough British corporate debt out there to buy. The Bank would have swallowed up the entire market in a matter of weeks.
I've mentioned before that a number of observers have called for the Bank to extend the range of the APF: notably the IMF, Martin Weale, and Danny Gabay of Fathom Consulting.
The emphasis on gilts has put the Bank rather out on a limb relative to other central banks - notably the US Federal Reserve, which has been able to purchase a much broader range of assets under it's "credit easing" policy.
But, as Adam Posen, the newest MPC member, pointed out in his speech of 26 October, it's a function of British companies' disturbing dependence on the banking system for its funds. In his words:
"[T]he financial system in the UK doesn't seem to have a spare tyre for the provision of capital to non-financial businesses when the banking system has popped a leak".
That lack of a corporate bond market, he said:
"[R]eveals a major long term structural problem in UK financial markets which could be of potential harm as the UK economy begins to recover".
In its statement today, the MPC pointed to evidence that its policy was working. And the evidence is there: gilt yields are undoubtedly lower than they would have been without QE, and bigger companies are using that opportunity to issue debt on a larger scale than in the past.
But, as the MPC themselves note, the key question for the recovery is about the banks: whether they will ultimately provide the credit to finance a healthy recovery.
This has been a recurring theme here - I won't belabour the point. Just to note that, if the economy is recovering, now is the moment of truth.
Until now, the commercial banks have been able to say, with some justice, that the lack of lending is due as much to low demand from firms themselves as to insufficient supply by banks.
As a rule, companies don't want to take on a lot of new debt in a recession. But once things are looking up, they will be going to their banks for more working capital, or loans for new investment.
If the banks are demanding much tougher terms and/or limiting the amount they will lend at any price, now is when that constraint on the recovery will kick in.
We will wait and see - and so will the MPC. But in the meantime, many economists who supported the QE policy are left feeling a bit queasy that so much is being rested on an asset with such an uncertain relationship to the broader economy.
Thanks to QE we do not really know what the "risk-free" rate of interest is over any length of time into the future. All the city knows is that money is (almost) free and there's an (almost) unlimited supply of it.
We talk about it being hard to spot the impact of the Bank's policy (and that of other central banks). But in a sense, that's crackers. You can see the impact of easy monetary policy everywhere.
Across the global economy, cheap and plentiful money is doing wonders for asset prices. It's also making it easier for governments - especially the British government - to borrow an enormous amount. It's even causing headaches for emerging market governments, as they struggle to cope with shedloads of incoming investor cash.
But I'm sure the MPC would like to be able to point to more visible effects of its policy closer to home - for households and businesses in the real economy.