Library Thing/Good Reads

I am enjoying reading "Nella Last's War". It's the diary of a housewife in England during the Second World War. It's fascinating because it's this woman's actual life, not fiction. I don't think I've seen it mentioned on other blogs and I'm wondering why it isn't more widely read. That, however, is for another post, not this one.

I've noticed lately that many of the blogs I'm reading have Library Thing and Good Reads buttons on their sidebars. I don't know much about either one so I'm hoping some of you will be willing to fill me in. If you have a few minutes to spare I'd like to hear what you think. Do you find them useful? What are the benefits? Would you recommend one over the other? Is there any point in joining both?

I appreciate your input!