Yes, we are. And it works. It's difficult sometimes, but it works.
We have a set amount set aside for everything, including clothing, meals in restaurants, "impulse" buys, etc. And I have to do what I can do make sure that I stay within that budget. Most of the time, I can, but sometimes when there are good buys at the grocery store, my grocery budget gets a little out of whack for a week or so. And then I have to get back on track.
Right now, our cat budget is weird because of Tabby being here. We're spending a ton on vet bills for her ear mites problem and buying cans of kitten food and we weren't planning on that when we did our budget last December. Then she'll have to get her kitten shots and then in about four months or so, she'll go in for her spay. So the cat budget is a little out of control, but I'm careful to make it up in other ways.
DH and I made an agreement several years ago that if something we want costs more than $50, we talk about it before we make any decisions. That way, if there's something on eBay (like something for my kitchen) that I'd really like to have, we'll discuss it before I do anything. Likewise when he's away on union business, if he sees something he'd like to have, he'll call me. We have to agree on it before the purchase is made. It's a rule in our house. Most of the time we will agree, but there have been times when it's simply not an option to buy something at that time.
It works for us...I don't know how, but it works.