You post in a thread, it goes into My Threads. If its blue, it has not been posted in since you last signed on. If its black, it has. Its not that difficult to understand, I don't think.
I use My Threads all the time.
The only thing I wish would be of change is what Holte said, the option to add one to your threads without actually having to post in it. Like under Quote Reply, add a My Threads.