We do have plans for features that we think people will be happy to charge for. Right now, we're not ready to talk too much about those features, but we think there is real pain we can remove.
We feel validated by the fact that people love the features we have right now so much that many have asked if they can pay for them.
Free is a strategy. We'll let you know how it works out :)
Having said that though, what you have right now is a "nice to have" and it excites everyone for the soft value it adds. But I wonder if the current product can pass the Penny Gap. I know you don't think its meant to, but I am really not sure if the current users will be the ones who would pay for whatever it is that you will build in the future. Xobni is a good example of it. Dropbox on the other end is a great example of a free strategy that sold users on the same product that they expected users would pay for. Basically with a strategy where you acquire a lot of free users thinking they will pay for what they have not seen as yet, can be a dangerous one.