I like to cook. I have a few standard, signature dishes where I more or less freestyle every time I make them -- beef stew, chili, quesadillas, pasta sauce.
I also like to try new things. For example, I'll probably be making Tyler Hamilton's lamb shank Irish stew this weekend. So yeah, the first time I make something I usually follow the recipe pretty closely; and I find a lot of my recipes on the web.
But, at the same time I also own a fair number of cookbooks which I do like to use for their recipes and, more importantly, for a bit of immersion into a style or a philosophy or a technique. And I find cookbooks are still really great for that.
Interestingly, Adam Gopnik is thinking some of the same things in his recent New Yorker article, What's the Recipe? Our hunger for cookbooks.
Another answer to the question "What good is the cookbook?" lies in what might be called the grammatical turn: the idea that what the cookbook should supply is the rules, the deep structure--a fixed, underlying grammar that enables you to use all the recipes you find. This grammatical turn is available in the popular "Best Recipe" series in Cook's Illustrated, and in the "Cook's Bible" of its editor, Christopher Kimball, in which recipes begin with a long disquisition on various approaches, ending with the best (and so brining was born); in Michael Ruhlman's "The Elements of Cooking," with its allusion to Strunk & White's usage guide; and, most of all, in Mark Bittman's indispensable new classic "How to Cook Everything," which, though claiming "minimalism" of style, is maximalist in purpose--not a collection of recipes for all occasions but a set of techniques for all time.
If you love cookbooks, it's a great read.
FWIW, the most recent cookbook I've purchased is Michael Smith's The Best of Chef at Home: Essential Recipes for Today's Kitchen. I really like the way he sees his recipes as starting points for improvisation.