I have just listened to the co-founder of Twitter on TED and I was fascinated to hear about how twitter has evolved from the original idea and how people have invented new ways of organising and getting their messages across.
The @ and # symbols are just two of the key devices integrated into Twitter at a later stage.
The @ symbol allows to you to refer to people by their twitter username, i.e @gicela. You can use this at any point in your tweet and it’s also public.
The # tag is used to refer to a group of people following the same topic, for example a fundrasing event #Twestival or a conference #SXSW. You can create your own #tag to point to people to the same topic of conversation.
In the last week or two, a new service called wefollow has created a new Twitter directory based on people assigning ‘tags’ to themselves, e.g. #gardening, #biking, etc.
Visit the official support pages for more on Twitter basics.
Listen to Evan Williams on his TED talk, and the Twitter feedback at the end.