The following chart comes from the newly published The Credit Suisse Global Investment Returns Sourcebook 2013, written by Elroy Dimson, Paul Marsh, and Mike Staunton (first mentioned here).
The chart shows the real yields on inflation-protected 10-year bonds since 2000.
According to the report,
Even 20-year bonds, where they existed, had low real yields; zero in the USA, 0.1% in Canada, −0.1% in the UK, 0.6% in France and 3.4% in Italy. Abstracting for default and convertibility risk, investors, even over a 20-year holding period, will earn real returns of close to zero. For taxpayers, after-tax returns will be firmly negative.