I'm currently in private alpha with my Blackberry App. Is a panic button for Blackberry users in dangerous cities in Latin America (mainly).
I've been online for about 60 days, have done zero marketing, no push of the app and have around 300 active users. People seem to really like the app.
Twitter has been abuzz with people talking about it and in a few weeks I'm releasing the first "beta" version and will start charging for it. Lets see how that goes.
I'm starting my focus in Venezuela since I'm from there and know the market pretty well. The main problem is the government restrictions in my country to charge in a foreign country (in this case dollars) so I have to charge in the local currency, but there are no payment gateways... is very complicated.
All an all, I think the private alpha has been a success, so there you go :)