Seesmic was one of the first apps to hit the new Windows Phone 7 Marketplace, and while it's an interesting take on Twitter, especially with the new side-swiping design schema that Microsoft has favored for this mobile platform, Seesmic has a lot of work to do.
Instead of jumping straight into the timeline and lists of mentions, the top level shows multiple Twitter and Facebook accounts, and general timelines for trends, the Twitter directory, and a search window. The disadvantage is not being able to see your timeline right away. The benefit is easier profile management, since you can dive into one profile as easily as you can the others.
Seesmic's Windows Phone app is also adept at letting you post to multiple accounts and reply to all users mentioned in a tweet. Triggering the onboard camera to add a photo is no sweat, whereas Twitter goes only into the library. Seesmic also includes an automatic link shortener, which will be great when Windows Phone 7 gets copy/paste. It's great anyway, but for now you have to manually add links, an inconvenient limitation that's not Seesmic's doing.
The app falters in its lack of notifications, and it doesn't include automatic update options in the settings. Seesmic can handle replies, but it's inelegant when it comes to direct messages. In addition, the Settings choices were thin, and we received a fair number of failure and error notices getting started.
It isn't a bad app, and it's a free one, but you may prefer Twitter's official app. In the meantime, look for the improvements to Seesmic that are sure to come.