The views expressed in this post are my own personal (HRA protected) views, and are not representative of any organisation I have any involvement with.
I use it. It's quite good for getting back in touch with people you used to work with who might need, or know of someone, who would need your services.
I think it is worth being on as you never know what work may come of it. If you complete your profile it is a good way of promoting your business. It only takes a few minutes and may result in work. If not, you've lost a few minutes.