I think if Twitter hadn't resolved the downtime issues there could have been a mass exodus to Pownce, but Twitter took care of what they needed to and Pownce lost its opportunity. Even though Pownce had a lot of features that Twitter doesn't (filesharing, etc) I never really thought of Pownce when I needed to send a file, link, or image to friends. I always went straight to twitter and used TinyURL or mediafire.