Discussed a while ago. I think it is good (although it hasn't worked for me yet) as do the majority of the MBA class I am in. Strongly recommended by the School and most of the external speakers we have on recruitment too.
Great for keeping track of where people you know now are (and therefore knowing who might be able to swing you some work.) The rest - depends on your niche. I know people who have had work from simple searches on it, I have had work because people have tracked my current contact details using it. YMMV.