I'm a registered user of fitaly palm, and want you guys to succeed with the tablet pc version too. To be honest, I think the current feature set is something people would pay for. There are always more things people would want, but it's good enough now.
As for econmically viable. My take is that not enough people know about your product. You need more exposure. From the outcry that you guys got on the palm forum when you announced the end of development there and the responses you get here at the end of betas, it seems that you have very loyal users, just not enough of them. Please take this commment in the intent it is given, but you guys need more marketing effort and not more technical effort if you want to make money at this point.