I can't possibly be the only person who just writes in the cookbook itself? No?

Cute, but mostly just a gimmick.

They're less good for marking recipes you want to try if their sticky edge is on the top. If so, you either need to turn them sideways or have them tab out of the bottom of the book/file/cards -- not so handy. I usually use tape flags to mark recipes; they're cheap, are easy to color code, and you can write labels on them if you want.

I also pencil notes right into the recipes themselves. That way, I'm not going to miss a change because I forgot to cross-reference with a post-it note.

Yeah, flags work better for me too, and I always write my notes in the book itself (well, if I remember to). Not only do I find that more helpful, but I know when I read through my grandma-in-law's old recipe collection and see her notes (and doodles!), I get a kick out of it, so maybe someday some descendant of mine will get something out of seeing my notes. :)

I really love this idea. When I'm developing and adjusting recipes at work, I can go through stickies like crazy! These can better organize my "jots" So I don't have to write out "use less of this," or "add more of that" which works for me.