I posted this in another thread - it is nothing groundbreaking but would be a good small project for someone to tackle:
Simple Ruby gem I was surprised didn't exist (that I could find): `validates_twitter_username`
Given user input for username, ensure it is valid. Two levels of verification - one would be probably regex based that the username matches twitter restrictions (valid characters, length less than 15), one that pings twitter to confirm the account is registered. Appropriate ActiveRecord errors etc