I just recently launched my free Twitter bookmarklet app called BigTweet http://bigtweet.com and got my first review http://bit.ly/TiPs
I'm interested in pursuing the freemium model and would like to begin working on some "pro" subscription based features for interfacing to Twitter. Should I let BigTweet grow on its own and work on the advanced features, or spend most of my time enhancing the free version and develop some viral components?
How much time do you spend on developing versus promoting?