What does a negative interest rate really mean?

I am reading more and more about negative interest rates, and so I figured it was about time I got my head around what that really means.
As you might imagine, what it means is that instead of earning money on your bank deposits, the bank charges YOU for the privilege of lodging your money in their hallowed halls. This kind of charge on savings sounds counterintuitive, and in a way that's actually the point of it. The idea is to discourage the hoarding of money by commercial banks and drive them to do more lending, thereby increasing spending, stimulating economic activity and boosting GDP growth.
Although historically the concept was not really taken very seriously, it appears to be an idea whose time has come. A number of countries have recently introduced negative interest rates, starting with Sweden in July 2009 and then again in July 2014, followed by Denmark in July 2012, the European Central Bank in June 2014, Switzerland in December 2014 (the Swiss has actually tried it before, way back in the 1970s), and, most recently, Japan in January 2016. So far, at least, the negative rates remain relatively small (0.1% for Japan, 0.3% for the ECB, 0.75% for Switzerland and Denmark, and 1.25% for Sweden). The big players here are clearly the European Union and Japan, but both the USA and, yes, Canada are currently giving seriously consideration to allowing interest rates, already low, to dip below zero, and Israel, Norway and the Czech Republic may also follow suit quite soon.
Bond rates are also affected by this trend, and an estimated 27% of global government bonds (some US$5.5 trillion) are now trading at sub-zero rates, so that investors are actually having to pay to keep their hard-earned money in bonds. Investors may still opt to buy such bonds if they think that the alternative - such as falling equities or even higher bond prices in the future - are even riskier and less appealing.
You might say that you have not noticed any high street banks advertising that they are now charging people for their deposits, but one, they probably would not go out of their way to advertising this, and two, thus far the negative rates are only being levied by central and national banks which lend money to other commercial or retail banks, and even then only on a relatively small slice of the money they lend. Technically, the retail banks could turn around and pass on these costs and start charging individual investors and ordinary savers, but so far they have not done so. While the negative rates stay relatively low, and look as though they will remain temporary, the commercial banks will probably avoid the bad press of charging customers for their deposits, and will just swallow their higher costs. But there may come a time when that may change.
So, does it work?
European and Japanese financial planners seem to think so, and some are calling for a yet stronger commitment to negative interest rates so that the effects can properly take hold on the economy. They point out that the near-zero rates of recent years have only resulted in lacklustre growth at best, and something more dramatic is needed to shock economies back into action. Furthermore, they note that the warnings of some critics that banks faced with negative rates would just keep all their money in hard cash, paying zero (but not negative) interest, have not actually come to pass. The banks are finding it easier to put up with mildly negative rates than to have to deal with huge piles of paper money.
But critics point to the recent nose-dive of European banking stocks, and to weakened currencies, as examples of just how risky a ploy it is. Banks, they argue, just cannot prosper in such an atmosphere, and banks, like it or not, are a mainstay of the world economy. They also note that the experience in Europe and Switzerland at least has so far failed to boost growth there, although these are perhaps still reasonably early days.
In short, as is so often the case, the jury is still out. It is a risky policy, certainly, but policy-makers are running short on alternative ideas. Either way, the grand experiment seems set to continue for a while at least, possibly right here in Canada.