I think one important component to the success of M-Pesa is Safaricom's near-monopoly on the mobile telephony market. If you are not the only big player in the market it's going to be much harder to get your mobile money network running straight away because you have to think of support by other telcos and competition on pricing.

I spent some time in Kenya and M-Pesa is very practical, I used it regularly for small payments. One thing that I found a bit frustrating is the very high transaction costs - way higher than you would ever pay with regular banking. The (poor) users don't really have a choice though, so Safaricom is able to make massive profits.