Yes, it's worth learning, I first bothered with it using a Lynda tutorial last spring and used it quite a bit but I have forgotten most of it now. Hence, why I am struggling with it and asking questions on here. It's not perfect and I'm not sure what changes will come in with version 4.
My only advice would be, make sure you have a good grasp of HTML and CSS before learning it, and not as vital, javascript and jquery.
I'm very rusty and learn as I come across problems, i am struggling with some things and my HTML and CSS knowledge isn't great anymore, having to google a lot of things to see what they do.