Since the latest update of Twitter for iPhone, it doesn’t correctly sign you in to Favstar.
A change introduced in Twitter for iPhone 4.3 kicks you out to Safari on the iPhone, and logging in does not return to Favstar properly. This Twitter bug may get fixed in a future version, as it is affecting more than just Favstar.

In the meantime, we recommend trying out Tweetbot for iPhone.
Tweetbot uses our API to ensure that Favstar pages work properly. Your currently-used account will be automatically logged in to Favstar when viewing a page. This works even when you’re using multiple accounts.
It’s possible to easily favorite, retweet, and award tweets of the day from within the app. For the avid Favstar user, it may just be the best choice. We’ll have a rundown of all the ways to use Favstar from within Tweetbot in the near future.
