Unleashing the ideavirus: a conversation with Seth Godin: "[D]on’t forget that the ideavirus follows a life cycle. Your job is to decide at which moment you will shift from paying to spread the ideavirus, to charging the user and profiting from it."

Timing is very important to the successful introduction of a paying service piggybacking a free one. The more you wait, the more people get used to the free lunch and expect it to remain so (or even feel they have a right to it). Maybe starting free and paying options right from the start would alleviate transition problems. Companies would still have to properly position them one against the other (give enough but not too much for free).