What makes your application different from others? I strongly feel the user experience that you provides plays an important role to be successful. Some of us might have felt that(at least myself), you woke up one day with a brand new idea but later you realize that somebody had implemented that an year back. Which is a frustrated feeling, I have been to that situation so many times. So even if that idea exists already, how to make that idea a successful one.
Say if you are going to enter in to a world where there are n number of similar applications, how will you attract the users? A great example may be GMail, IMHO they entered to the party when Yahoo and Microsoft where ruling email market. But now GMail is much popular than other email service providers. One reason I could think of for this success is the experience that you get as a user.
Not sure whether anybody has noted this or not but today when was about to send an email to my friend, I got a message box saying Did you mean to attach files?
Yes, GMail reminded me to attach the file. I was surprised to see this, GMail has intelligently scanned what I have typed in the email message and gave me suggestion before sending…. WOW!!!!!. I checked whether Yahoo mail has got this feature, not yet. That makes GMail stand-out from others.