Tweetfave is a simple service I built to solve my own need: to be able to mark tweets with interesting links for reading later or bookmarking. Tweetfave periodically checks your Twitter timeline to see any new tweets you've marked as favorites (now known as "likes"). Those tweets are then sent to your email inbox for your review at a later time.
On my blog I've described some aspects of building Tweetfave and periodic updates on usage numbers:
Status updates from the @TweetfaveApp Twitter account:Tweets by @TweetfaveApp