Twitter Annotations was for me the most exciting announcement of last year - structured data is everything - and the idea behind annotations was to allow arbitrary data to be attached to each Tweet to allow more exciting applications to be built.
Currently Twitter is still limited to the kind of use cases that the data associated with a Tweet allows. With Annotations a tweet can contain the meta-data to describe the meaning of the Tweet.
So for developers what could be built would be limitless - so if you want to build a Quora clone - by having the Tweet as the question with all the topic data stored in the annotation.
Game developers could build who new social games by storing game status information within each Tweet - so for instance the current positions of pieces on a chess board could be stored in a Tweet. So as you play others could look at the status update and see what move you made.
I viewed the announcement much in the way when Facebook released its App platform - that for me was one of the pivotal technology changes they made that allowed such growth.
I hope we see Annotations in 2011
(originally posted in answer to this Quora question)
Looking forward to Twitter Annotations in 2011Read more at nickhalstead.com