The 5 B Rating System
I'm not a particularly sophisticated reader and I'm certainly not a sophisticated reviewer. Other people write synopses and make the book relevant to both the genre and our wider culture, have all kinds of anecdotes about the time they met the author, find relevant quotes, and then go on to make some grand statements about how this book is or isn't a crucial piece of literature. I enjoy reading those sorts of reviews (when they're done well) but often they don't answer the questions I have when I'm looking for a book.
I'm afraid that I have a lot of demands on my time, and the sad fact is that I only read fiction when I go to bed so I get about 30-45 minutes of reading done a day. I read fiction purely for entertainment. I do not expect to get my worldview rocked or find any hidden insights into the human condition. I like violence and sex and iconoclasm and cynicism. I like stories with chrome plated starships, demons the size of shopping malls, smart sexy vixens and smart musclely heroes. I like stories about sadistic killers, backwoods inbred murderous hicks, cyberpunks bringing down transnational corporations and excorcists trying to make a living in the contemporary world.
There's several genres I like, but only few types of stories, plots and protagonists that I like. I like explicit sex and violence, dystopias, cynicism, and anti-heroes written to a high standard. It's easy to drop books into genres based on plot and setting, but it's not so easy to generalize based on "volume" or "explicitness". Yes, I know ALL about splatterpunk, but that's a genre that puts style over substance. I need the real substance of a good story, but I demand a style that's strictly for the grownups.
After a very bad week where I thought I was buying books that were for grownups (based on recomendations I got at a site that rhymes with Wood Bleeds) and discovering they were actually G rated YA books, I decided it was time I tried to do something for anyone else who might fall into the same trap. I came up with my "5 B's" system of rating. To make the alliteration work, I had to contort some of the terms to fit ideas they probably shouldn't.
BLOOD: One on one, interpersonal violence. Includes shootings, stabbings, fist fights, point'n'click magic, etc. A score of 0 means nobody got hurt, a score of 5 means not only is there a lot of detailed violence but it's crucial to moving the plot along.
BOOBS: Sex. A score of 0 means everyone keeps their clothes on and sexuality does absolutely nothing to drive the plot, a score of 5 means the sex is explicit and prurient. Look at how the book is shelved for details on the nature of the smut.
BOMBS: Industrial scale, interpersonal violence. This would include things like ordering soldiers into battle, space navies lobbing warheads at each other, etc. 0 = As peaceful as a drum circle full of stoned hippies, 5 = full on interspecies galactic warfare
BONDAGE: Kinky/taboo concepts and relationships. Closely related to BOOBS, but not quite the same thing. A high bondage score doesn't mean explicit sex, but it does mean there are relationships - and methods of relating - that are considered taboo or kinky in the early 21st century, english speaking industrial world.
BLASPHEMY: Very closely related to iconclasm. A high blasphemy score means the concepts, and the way the plot is executed, would likely shock the sensibilities of someone who considers themselves to be a "god fearing christian". Different than bondage in that it's less about interpersonal relationships and more about values and worldviews.
 I don't really get involved in the nonfiction book communities; I'll leave that to the scholars and professional academicians. My conversations around nonfiction books are ancillary to the subjects themselves; eg I'll chat with my photography buddies about a good book to read about an aspect of photography but I don't look for ways to talk about the book itself.