Flickr for iPhone was recently updated to add support for iOS4 and the iPhone 4.
First, is support for multitasking. According to the update info in the App's description page, photo uploads will continue in the background. In addition to that, iPhone 4 owners will be happy to know that they can now upload HD video.
Users can also post their photos simultaneously to their twitter account via a flic.kr short URL.
The full update list is below:
New in version 1.2
– Multitasking support: Photo upload continues in the background
– Twitter support: Post photos simultaneously to Twitter with a flic.kr short URL directly from the App
– Support for HD video uploads
– Support for fast app switching: Come back to the App where you left it
– Enhanced full-screen browsing behavior
– Clear recent searches
Have a look at the App here: Flickr