The market will not support all these photosharing sites in the long run.
Twitter will be purchased or exclusively locked up in a strategic relationship by one of the companies that already has a photosharing set up/photo monetization platform.
Under that scenerio the acquiring company is unlikely to promote such a disaggregated approach to the aggreagtion of media in microblogging. If there is money to be made with Twitter it involves pushing people into monetizable experiences, like monetizable media destinations and transactions/etailing. (The social networks have finally figured this out e.g. MySpace/Citysearch)
Sure, there will still be boutique image hosters and tiny URL providers, etc. etc. But ultimately the world just doesn’t need 20 different places to dump your photos. The ones that will still hang around will be the ones most tightly coupled with the apps that encourage the uploading.