A little out of order, but...

What tools do you find useful?

YNAB has by far been the most useful for us. I always wanted to do envelope budgeting, but without direct import, it was too tedious for me to get everything in and be accurate. They added direct import at the end of last year, and it has been great. Even the wife likes it more than other systems we have used, which is the biggest plus.

Should one of the two of us be more in charge of all aspects of the finances?

In an ideal world, no. I check YNAB every morning at categorize any missed transactions as they come in. I watch everything like a hawk, but I enjoy it. I wish my wife were a bit more plugged in. She always defers to me. It is nice that she trusts me, but it would be nice to get another opinion from time to time. I have friends where both husband and wife are equally involved and motivated, and it makes me a little jealous at times. If you can get both involved, I think that is best.

How often do you and your SO sit down and go over finances

We talk about it regularly. A lot of it is because I'm asking how I should categorize transactions she has made. It is never accusatory, and that keeps the conversation regular and easy. We'll definitely have a big year-end sit down to figure out how we did and what changes we are going to make for the next year. From time to time, I might mention to her that we are spending a lot this month, and we need to cool the jets. Luckily, the wife is pretty responsive to this.

Any other tips?

We have only one checking account. We co-mingle everything, though we do set aside money for each of us to spend on whatever. Also, I feel you on the lifestyle creep. We talk about it a lot. We try to verbalize what we see going on to get each other's perspectives and make sure we are on the same page. This can be about ourselves or about friends and neighbors of ours. We try not to be judgmental, but we'll have conversations along the lines of, "so and so bought a new car. Looks cool, but I'm so glad we don't have payments. Aren't you? I'd rather save it for XXXX goal. What do you think?" Lastly, being super frugal every month is hard and can get tiresome (I compare it to trying to sprint all year long instead of pacing). Instead, we kind of have a normal flow to our spending, but about 2-3 times a year we try to really tighten our spending for a month, and get back to basics. We eat out less, go out less, and we don't buy some of the discretionary stuff we normally would. It is a good way for us to sort of reset and fight that creep mid-year, and because it is only for a month, it is easier to stay motivated. We also usually save a few hundred bucks each of those months, which helps.