I think of money as a platform. And getting people to use ComplementaryCurrencies [CC] is a platform migration problem.
|| Barrier for potential users || Possible Solution ||
|| Don't know it exists || Publicise. Find ways for users to advertise ||
|| Don't know it's virtues || Publicise information about why it's good to use. For example, if the currency is designed to avoid inflation, publicise the inflation rate using the currency. If designed for egalitarian ends, publish distribution of wealth within the currency network. Publicise the size of the economy in terms of number of transactions. ||
|| Can't assess prices || Websites can offer autoconversion of prices into NationalCurrency [NC] equivalents. Vendors can publish equivalents. Third parties can publish price comparisons. ||
|| Can't find people who use it || Find ways for users to advertise that they're users. eg. LETS directories, online markets, description tags on weblogs and social network profiles. ||
|| Can't find things for sale || Similar to above, but emphasize online markets, classified ad sites etc.||
|| Can't get the currency || Provide a bank who will sell it for other money. ||
|| Worry that currency will be useless || Allow users to sell the CC for the NC ||
|| Worry that currency will lose value || ||
These recommendations are ways of removing the barriers of entry to encourage use. They aren't always appropriate. For example, if converting to and from the national currency is too easy and transparent, then the CC won't be able to preserve some of the properties which make it different from the national currency. And problems with the national may be able to infect the complement.
Also, providing a bank able to trade the NC for the CC may be hard. If conversion is too easy there's the obvious danger of a run on the bank, which will go bankrupt or have to catastrophically devalue the CC.
The BlackMarket likes bigger notes, which are easier to hide. A strategy? :-)