While I have suggested several "solutions" to the problems facing current coinage and currency it won't be long I am afraid that none of the various solutions will really matter. Coins and bills will most likely go the way of the vinyl record album and cassette tape and be replaced with virtual money. Debit and value cards will be like CD's, an interim if not ubiquitous solution until some sort of biometrics take over for the majority of transactions.
What will really seal the deal on cash transactions will be like so many other innovations. The criminal and

elements will drive a cashless solution much like

created the home VCR/DVD market and then mainstream users will buy in. Later on that will evolve to something akin to iTunes' takeover of music purchases.
I see people these days, especially youths, use debit or credit cards for purchases that would shock the older crowd. Why use cash to buy a can of pop or a candy bar, just whip out the plastic. No signature needed under $25. I already have people want to use PayPal for small payments all the time.
It's coming folks. Diehard cash users will fight it all the way, these are like the guys who still prefer 8-tracks in their T-Top Camaro.