I just signed up for an interesting social aggregator website called Jaiku. It has the same functionality as twitter, but it can subscribe to and display your RSS feeds. I'm not sure I'll use it as much as twitter, but it seems like a useful application. You can check out my Jaiku page here. I heard about it via a twitter from Jason DeFillippo, who was waiting to get in to the Jaiku launch party in SF, but apparently ended up leaving with Scott Beale due to the long, motionless line.
Update: As it turns out, but Scott and Jason made ended up going to the Jaiku party, as evidenced in this laughing squid blog post.