Not sure if the old Live Thread used to lag after a few hundred posts were made, but I had pretty bad lag when I exited the compact since all the posts were rendering. I might make it cap and hide the posts in the background and limit it to the last 10 or something sometime in the future. Tons of stress testing needs to go into it, but you're all welcome to break it in the live thread tonight.
But if you do find a problem, state the problem, don't just say it's crap and broken. It's beta, it's meant to be crap and broken in a few parts, but the main parts are functional. It was either release it now as beta or leave it a few more weeks for a stable release, preferred letting you test it out now to catch any problems early on.
One thing to note: when you send a message, it's not going to instantly appear. This is because it sends the message to the server and only displays it once it has confirmation from the server that the message has been saved. This is to avoid making you think a post has been saved when it hasn't. In the future, I'm going to make it show the post instantly but display an icon if the message failed to save on the server.