I'm on GR a lot, and member of several groups related to my writing and reading interests. GR reviews can be good, but of course can be rubbish too. On the other hand I've seen a lot of very unreliable reviews on Amazon too, quite a lot so obviously biased that they have to be from the author or associates. @Poziga - if you go to the book's page, there is a list of genre votes on the right side of the page.
Thanks @Bryan Romer , I thought that was just a list of genre with the number of people that tagged themselves with. Like they choose their favourite genres and that this was just a list of randomly chosen genres... I don't know why...
I use it every night, I love seeing how many pages I read per day, and how quickly I finish a book. Not many people I know are on there.
I always have a look at it and I tentatively want to join. It seems good. I mean, it appears to rate books more clearly than say if you posted it to facebook or a wider social audience. It seems to be a place where books get judged on knowledge specific to people with knowledge in the area (writing, reading), rather than general consensus and media/commercial influence.