For micropayments to work however, I guess one would have to actually create a game which is so enticing that the players will return again and again, and will want to spend money to get an advantage, extra levels, other characters or other things which could be sold seperatly. I have found a list of ten ideas of microtransactions in games. There are some good advice there, I must admit. I will ad one of my own here:

Create a game with a montly highscore list – the winner each month will win the ultimate prize (and if you could get this sponsored from somewhere… Even better). You will then let all players buy all the advantages they want… Beware however, I don’t know if this is legal or not – I suspect that it is not ok in Denmark, where I live.