For me, I'd like notifications whilst on the move, rather than having to load up my web browser and load the site, log in and check then.
Saves time and money on 3G for me.
Also, having it as an app, it'd be easier to load up pictures, although most use 3rd party websites and apps like Photobucket, there's still quite a few who can't use them.
This will help with hunting reviews, classifieds and even profile pictures.
Quite a few features to consider.