1/3 to property owner, 1/3 to historical society, 1/3 for me. I buy small treasure chests for property owners, and fill them with the finds I have dupes of or thing I know will make them happy (mercs, Rosies, wheat pennies, etc). I keep early copper and silver coins and the best colonial era artifacts, unless the latter has some significance to the town. I also give the owner a history of their property and use the objects I find to provide examples. Of course, some people insist that I keep everything, which is nice.
This has led to a talk at one historical society, and people contacting me with invitations to come to their historical homes, cellar holes and/or farms to do my thing. I also have formed some nice relationships and a solid reputation/references when I do contact folks by letter to request to dig. I have free reign to hunt at my convenience on over 2000 acres and a few dozen properties which contain the earliest European history in our area.
I was always honest and generous with folks, but after meeting a completely selfish and unscrupulous older detectorist earlier this year (never shared with or compensated owners, hunted without permission, etc) I became committed to my approach. I want to be trusted and free to roam 10 years from now, with a clear conscience, and a love for history and objects that is never stronger than my respect for people. I have become a steward for local history, not just some guy squirreling everything away for myself.
I have to say, I love how things have gone so far!