It will not work - because there are another currencies without demurrage.
One can just switch to another currency for saving and then back for spending

How do you get people to do this? If I'm getting this right, either you have to find a way to force them to do it, or they have to voluntarily choose to take part in this system on ideological grounds. I'm sceptical of solutions that rely on ideology - they lose out to more pragmatic approaches in the end. Maybe I don't understand what you're proposing to actually do?

If the demurrage rate was small enough, then it might work, but it would be no different in practice than the fees system.  Either way, the over-parity bitcoins end up in the possession of the miner who found the block hash.  Without looking into it further, one possible problem that I can see is that demurrage rates would be detached from actual block creation, so it's possible that they could occur at significantly different rates, resulting in an unbounded monetary base.  Also, demurrage would also make free transactions impossible, and that would be bad for shifting funds around personal wallets, donations and such.

I don't agree with your viewpoints here.  Transaction fees are and will be a market.  Currently the market price is zero, pricely because network data volume is relatively low, and therefore the cost to the network is almost zero.  There are some limiting factors on the growth of the blocks, however; both intentionally in software as well natural limits due to scale of the network.  As the transaction volumes increase, the average fee will also increase dynamicly.  Some people will be trading in a manner that requires that they get rapid verifications for the transactions, and they will need to provide higher average fees to encourage miners to include their transactions.  Others will be trading or donating in a manner that does not need quick verifications, such as a trade with mutually trusting parties, donations to a charity, or very small purchases; these transactions will not pay transaction fees nearly as high, or not any fee at all, due to the fact that they can wait for days, even weeks, for inclusion into a block.

Nor do I agree that this is a commons situation.  If it were a commons, there would be a resource that can be extracted, without additional costs to the node, without any practical limits; which is not the case here.  Every node must contribute to the overall network just to participate, but not at an equal amount.  In the future, some nodes will be 'lightweight' clients that receive full blocks, but then trim their blockchains for their own needs, keeping only the 80 byte headers to verify transactions that relate to their own trading activities, but neither generating nor maintaining full time network connections.  Also, 'ultra-light' clients that keep no blockchain of their own at all, and depend upon network connectivity to a trusted provider capable of verifying transactions on their behalf.   Neither of these two types of nodes contribute much to the network, nor do they require much; but they give what they get.  Most users will likely use such lighter clients in everyday life, and the majority of the network will be supported almost entirely by the generating clients and other full clients whose owners have their own reasons to participate in the network as a full node, such as bitcoin 'banks' like Mybitcoin.com and verification services for the 'ultra-light' clients.

So, wait, you want to destroy money in order to avoid the effects of destroying money?!?

Interest isn't evil. It's simply the profit made in exchange for keeping safe or allowing someone to use money. If you disagree with the amount of interest charged or offered, use another service.

Also, some of us don't see deflation as a problem, either.

I'd much rather have a currency which increases in value than one which devalues.

Dude, put down the kool-aid. Keynes was WRONG. And he knew it.

I say again, If you don't like the interest charged or offered, use another service.

Given the prospect of choosing a deflating currency or an inflation currency, I think people would choose a deflationary currency.

Of course the arguments against deflation have been used to defend inflationary policies. I'M NOT DEFENDING INFLATIONARY POLICIES.
I DON'T LIKE BEN BERNANKE NOR WALL ST. Criticizing deflation doesn't make me an inflation advocate just as criticizing the Rothchilds doesn't make me a nazi.

Deflation discourages commerce. I'll try to explain it with an example.
If you can buy an apple today with a bitcoin and two apples tomorrow with the same bitcoin. Why would you buy anything today?
Maybe I'm missing something.
Does deflation encourage commerce? Can anyone explain me how?

I'm sure you can think of a few reasons if you try.