As it required minimal effort on my part and might someday help someone get in touch with me, I've turned on LJTalk.
As with the other IM-type services I use, I'm just going to leave it logged in all the time. Feel free to use it if that's convenient for you.
I'm experimenting with the feature that lets some notifications come as IMs rather than as emails....it's a nice idea; we'll see if I actually end up liking it.