Personally, I like to house rule that there's no XP penalty upon losing a familiar as long as it's not abused ("Hey Softy, check that trapped door for me"), and shorten the time to get a familiar back to about a week. That way the liability issue goes out the window.
And to address the question, not much. There was once when my tiny earth elemental familiar (Softy) the DM allowed me to take turned invisibile to spy on some people, and another time he helped move some rocks. But otherwise, he was mainly another personality to bounce my character's off of. Though, I did have a very-short lived character with a rat familiar that I had conceived of using to snoop and ask around town.