Twitter apps can do almost everything that Twitter.com can: search Twitter, follow and unfollow users, and even manage Twitter lists (well, only a few apps so far).
One thing Twitter Apps couldn't do though was search for other Twitter users that could be interesting to follow. This is what "Find People" on Twitter.com does, but the microblogging company never extended the feature to third party apps.
That's changed today though. A few hours ago, Twitter announced to developers that it has launched the Find People API to fix that problem. Perhaps a tweet from Twitter CEO Evan Williams explains best why this development is important:
"Oh good, a find people API: http://http://bit.ly/dDvy8 If you wondered why you can't search for people from Twitter apps, this was the missing link"