Not to one-up everybody, but I have two sets of twin girls that are almost exactly three years apart. My older girls are 10 now, the younger ones are 7. The first set of twins wasn't really that difficult. We do have lots of family that live nearby that were willing to help, so that was nice.
When the second set rolled around things got interesting. For a few days we had 4 kids aged 2 and under, LOL! That period of our life is kind of a blur. I was working way too much and things were crazy with that many little ones. But we managed, and generally had fun doing it. Twins are really nice when they get old enough to play with each other, built in playmates! However, my 10-year-olds are rapidly turning into pre-teens. I'm dreading the days in the future that will be dripping with estrogen fueled meltdowns.
Fortunately my income is enough for my wife to stay at home, so it wasn't a financial burden.
Also, I know everyone has opinions about childcare, but putting our kids on a pretty strict feeding/sleep schedule from birth really helped us. Having both babies on the same schedule allowed my wife and I to get some much needed sleep during those early months.