For my family, I find the interest rates aren't enough for us to keep our sinking funds in a bank. I (I do the finances) do much better collecting the cash in envelopes. I love seeing it grow and don't want to touch it because of all the hard work we put in to saving it! I have envelopes for anything that requires planning.... seasonal clothes, Christmas, School related stuff, snow tires, etc.
We do have a few bank accounts for the big stuff, like our EF and vacation.