Writing this is a hurry but the furore over Allods has further strengthened my believe that there are numerous flaws in the typical Free to Play model. One major flaw is that a small number of players must pay a lot in order to subsidise the majority who pay nothing. Another perhaps more serious flaw is that in order to force people into the cash shop developers have to design inconvenience into the game. Making your customers suffer is surely not a sustainable business model.
Given all this I wonder if the pay for time model as used in China would not be a better approach. You could still incorporate a free to play component - think of it as a form of extended free trial.
Try the following:
Free players can play for up to 10 hours per week.
Additional playing time can be purchased in lots of 10 additional hours at a cost of $5 for 10 hours.
A lump sum payment of $45 buys 30 days (or perhaps a calendar month) of unlimited playing time.
Perhaps further discounts may be available for higher quantity purchases.
No cash shop. No items which give in game power increase.