Money stuffed into a mattress that gains in purchase power i.e. http://www.inflation.eu/inflation-rates/europe/inflation-europe.aspx indicates Euro inflation as being -0.1%) is so much easier than having to find bank/savings deposits to have money appreciate with inflation (maintain purchase power) and where the state might be applying a tax to the nominal 'gain'. 10% inflation, 10% interest, 25% tax on nominal 'gain'. (I appreciate your tax system is different).
For the century or two before the mid 20th century there were typically equal amounts of inflation and deflation, neutral overall (but in a volatile manner). Since then however there's been predominately just inflation (more or less since having broken away from the gold standard). Inflation is better for the taxman as they can erode your wealth by both taxation and inflation. For investors deflation isn't so bad as money stuffed into a mattress can retain or even grow purchase power without tax/inflation eroding the value.
Under such conditions is can be beneficial to be a borrower (debt) rather than a lender (buying bonds). Again leveraged ETF's can help there. If a leveraged ETF receives a $100 investment from you and borrows another $100 to buy $200 of stock exposure, and the cost of that debt is very low then you're in effect benefiting from that low cost debt.
As each of the US, UK and Euro are seeing negative inflation (deflation) hard cash/currency can be a appropriate holding (negative yields elsewhere - paying to lend), diversifying that hard cash can be a reasonable safety measure. Hold some bills/currency in each of a range of currencies (US$, Euro's ...etc). That way if any one of those does run into difficulties your exposure/risk is lower than having held all in a single currency and seen that currency being hit.
We're living through a era of where the return of money is considered more important than the return on money. Nothing new. Rather its just been a while since such a era was last with us.
Also, in looking at trends it appears that it has been falling in recent years compared to back in the 60s and 70s.
Nonetheless, it might be wise to assume some level of real inflation exists. One could take the FED's desired rate of 2% but, given that they have only come close to that about 8 times over the last 30 or so years, I think it might be wise to use a figure of ~2.5%.
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