I'm another candidate for the OCD bookmarker. My system for recipes takes advantage of the fact that Bookmarks display alphabetically, so starting certain kinds with the same letter keeps them together as a category.
They include:
c.[cookbook title/author] for recipes that interest me from a particular cookbook; I usually mark these when I first obtain a cookbook (via purchase or library); they're the much tidier electronic equivalent of the sticky notes I used to use to flag recipes in a given book.
i.[ingredient] By far the largest category of Bookmarks, they've saved me time and again when I review the fridge and pantry, or come home from the market.
r.[type of recipe] Examples: r.slaw, r.gingerbread, r.polenta, r.tomato jam... These are various versions of a dish in my cookbooks or online. Repeatedly, I've found that reviewing different recipes for the same or similar dish will enable me to develop a synthesized "best" recipe, or sometimes to reject alternate versions and choose a "best" to stick with. Sometimes they're a snapshot of interesting twists on a basic dish.
m.[season/occasion/cuisine] Dishes that work well together for a menu: m.Indian winter, m.Mexican summer/fall, m.J's birthday 2014, etc.
z.[personal experience] z.made is the largest collection among these bookmarks; z.on deck is an often-changing "short list" of recipes I really will make soon, z.never again (small but important), z.online recipe (ones that I've clipped and indexed that are part of the EYB Recipes available to all; currently this is the only way to track one's own, other than manually), z.annual Guild picnic, etc.
For books, my Bookmarks note the two locations in the house where stored, 'kitchen shelf' and 'sitting room'; these are the ones that I search within when preparing to cook. Other Bookmarks for books note where books of interest are to be found: library - checked out, library, Jan, Mary, etc. Wishlist Bookmarks group books I'm interested in by subject matter: home/seasonal, entertaining, preserving (broadly conceived), and reading. Only a quarter or so of the books on my EYB Bookshelf are actually here in my possession. Having wishlist Bookmarks has made it much easier to resist just buying every book I'm interested in. as it allows for review and prioritizing. There's a 'wishlist' Bookmark that is restricted to my top five to ten lusted-for cookbooks -- very helpful for birthdays and "letters to Santa".
ETA: Like others, I have a 'not yet cooked from' bookmark that I'm gradually emptying.