The iPhone app [iTunes link] seems to be an extension of its browser-based sibling. For example, check out the live preview mode pictured at right. You can also manage multiple accounts, post, upload multiple images at once (awesome) view stats and more. The UI looks nice as well.
While bloggers on other platforms have had compatible apps in the App Store for a while now, this is Squarespace's first solution. We're eager to play around with it. Squarespace for iPhone is free and requires a paid Squarespace account.