Bank savings accounts are paying less than 1% so let's not even count those. Let's start with a 1-year CD at the current "high" rate of 1.2% APR (
http://cdrates.bankaholic.com), on the assumption that you want to spend your interest, and not have it locked up for more than 1 year.
If you have $100,000.00 invested in those kinds of CD's, you'll earn a bit over $100 per month (www.bankrate.com/calculators/savings/bank-cd-calculator.aspx). The total interest earned is $1206.62. Not bad, and I agree that you spending that money helps the economy - a little.
Now, regarding this latest move by the Fed... is it going to lower those CD interest rates to zero? Let's get dramatic and say it halves it, to 0.6% APR. Now you've got about $600 less annually in which to pump up the economy.
Multiply that by an unknown number of individuals who have enough liquid savings to currently generate in the neighborhood of $1200 annually, and there's your total impact to inflows due to lower interest rates on personal savings.
But you know these are all unrealistic assumptions. At current rates, only very wealthy people can live off their savings, and anyone else that can generate meaningful monthly or annual interest are lucky, but oddly choosing to invest high amounts in cash-equivalents rather of bonds or equities. Few would consider that good money management. But again - if you're really wealthy, that might just be a sliver of your overall portfolio.
Bottom line: you might be really rich and this move by the Fed is really going to sting. If that's true - sorry to hear that. But you're rich, so hey.
I do, however, agree with your point about banks hoarding this additional available cash. Why aren't all those teabaggers frothing about these banks sitting on assets, instead of screaming at teachers, firefighters and policemen for wanting to keep their jobs and actually get paid?