Bond Funds - are they worth the fees they charge?

You certainly do not need an investment manager to hold your assets in cash, but should you pay a fund manager to manage your bond investments? and if yes, how high should the fees be that you pay for looking after this asset class.
An interesting article reviews this problem but we would rather have the investor focus on the fact that the selection of the right asset class (cash, bonds, stocks, currencies and possibly commodities, not to mention property or direct investments) is the main driver of long-term investment success.
Tinkering with the selection of assets within each asset class is an important challenge but should always play second fiddle to the selection of the right asset mix.