My letter grade system:

A = Outstanding. Highly recommended.

B = Very good. Occasionally has problems with proportions, ingredients, or technique, but successes greatly outnumber failures.

C = Has some good recipes, but also suffers from a great number of problems. Often can be more trouble than it's worth to try to cook from.

D = A disaster. Failures greatly outnumber successes. Not recommended.

F = Not a single successful recipe to be found. Avoid at all costs.

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Food Network Favorites: Recipes from Our All-Star Chefs , Food Network Kitchens, Jennifer Darling (Editor). (Full review coming soon.)
Suffers from the usual problems: poor editing, weak instructions, occasional errors with ingredient amounts or usage. Many of the recipes can be found in the individual chefs' other books. Bottom line: not a necessary addition to a well-stocked kitchen library. B-/C+

Off the Shelf: Cooking from the Pantry , Donna Hay. (Read the full review here.)
Very good ideas and interesting combinations of ingredients. Frustrating at times because of a casual attitude towards instructions and technique. Worth having, but the instructions need to be carefully reviewed before getting started on a recipe. B-

Sara's Secrets for Weeknight Meals , Sara Moulton. (Read the full review here.)
Very problematic, with weird combinations of ingredients, poorly-thought out instructions, a lack of photos, and some outright failures. Here and there it has a good recipe, but there are too many bad ones. C-

Everyday Italian , Giada De Laurentiis. (Read the full review here.)
A handy basic Italian cookbook with some excellent recipes. Occasionally suffers from sloppy technique and editing. B+

Fast Food My Way , Jacques Pépin. (Read the full review here.)
An outstanding book. Excellent recipes, clear instructions, creative ideas. The introductory chapter and dessert chapter are worth the price alone. A

Jamie's Dinners: The Essential Family Cookbook , Jamie Oliver. (Read the full review here.)
Very creative with strong ideas and tasty food. Fails in its accessibility; too often vague and sloppy when it comes to instructions and technique. For experienced cooks: B+. For kitchen novices: B-

Live, Love, Eat! , Wolfgang Puck. (Read the full review here.)
A good introduction to Wolfgang Puck's cuisine. Occasionally suffers from "restaurant-chef-itis," with too many hard-to-find ingredients or fiddly technique. Very good results if you're willing to put in the time and effort. B+

30-Minute Meals 2 , Rachael Ray. (Read the full review here.)
A better book than 30-Minute Get Real Meals, but not without problems. Italian recipes are good, everything else is risky. C+

30-Minute Get Real Meals , Rachael Ray. (Read the full review here.)
An attempt at low-carb cooking that's not satisfying to anyone, with serious problems in technique and bizarre proportions. A few good recipes bring the grade up to C-