I send at least one piece of (snail) mail everyday. No matter what it is - an invoice, a check, or even a birthday card, I stuff the contents in an envelope flaunting Endagon's logo, and put an Iced Tees stamp on it. Why do I do this?
Whether it's my local landscaper, pool man, accountant, or even my best friend on the receiving end, they not only instantly know that the piece of mail is from me, but they are reminded of my companies and services. The more visible your brand image is in the wild, the more people will know about you.
Go ahead and pick up some business checks with logo(s) on it and start paying your bills with branded checks. Then, stuff those checks in branded envelopes. Once again, why not?