Sorry to say, but the "low carb" category in EYB does not really work. Unlike categories like vegan or gluten-free which depend on a particular subgroup of disallowed ingredients, low-carb solely depends on whether the recipe writer labels it as such. And people have very different ideas of what is "low-carb". On the other hand, many recipes that are effectively low-carb (such as many salads and many meat dishes) do not get into the category because the recipe writer does not think the carb count matters.
For example, on the first page on my bookshelf in the EYB low-carb category, there are two recipes that are definitely not low carb. One contains bulghur, the other one is a jam that contains sugar, honey, balsamic vinegar and prunes. In addition, there are three recipes that I wouldn't eat on my low-carb diet as I don't think they're low-carb enough.
As a matter of fact, on my bookshelf there are 130 recipes that EYB has labeled low-carb, and 66 recipes that I myself have labeled low-carb, and the only overlap between the two are some personal recipes.
I think it would be worth considering making the bookmarks public. People are sharing lots of other information about their books already, and other sites like LibraryThing also allow you to see other people's bookmarks. Maybe it could even be optional. Yes, I know, your to-do list is big enough as it is, but I would think it a big improvement.