I've been having a lot of fun on Plurk, which is a social networking site. It's like really tricked out twitter basically. I love the scrolling timeline and how comments appear organized underneath each "plurk". I also really like the notification system they use. I'm trying to build up my friends list on Plurk - I think it could be about effective as twitter at promoting, but so far I'm having more fun using it to chat with people online than promoting my shop.
If you already plurk, please post your profile link so I can add you as a friend!