Mobypicture
Usability: 
i.mobypicture.com/ (xhtml-mp)
Mobypicture is a new service that lets you upload pictures from your phone to multiple social networks and blogging platforms including Twitter, Jaiku, Wordpress, Blogger, Tumblr, Livejournal, Brightkite, Facebook, Hyves or Vimeo.
Uploading is by MMS, email or a "browse for file" web form on the Mobypicture mobile site. When you upload a picture it's automatically posted to your accounts on all the networks and services you've configured in Mobypicture.
Mobypicture works well and seems popular, I'm seeing a lot of people using it on Twitter. I do wish it had better support for the embedded browsers on feature phones though. The problem is that the Mobypicture front page averages a whopping 250 KB thanks to 15 90 x 90 px image thumbnails. That's a lot of images and to make matters worse the images don't have their EXIF tags stripped so they are about 8X heavier than necessary. In its current form you need a smartphone or Opera Mini to be able to use the Mobypicture mobile site although you should be able to upload pictures by MMS or email from just about any phone.
