For a while, I got most of my lost discs back, over 50% return rate. The past year or so, almost none have come back; I think I got called about one Krait that the wind redirected into the lake. I ink all my discs with name and phone number.
Most unusual story with this was a white F2 Pro SL that I lost in or near the lake. Didn't find it, moved on. Some months later, in winter, a guy was trying to get a disc off the thin ice on the lake. This guy was going crazy, trying to climb a tree that overhung the lake to try to get a long stick on it. I tried the disc retriever with the string and another guy used a stick from the shore. We finally got the disc back and I asked what disc it was. He said he didn't know. When I looked at it, I saw that it was my lost P-SL, that he'd dyed over the name and number on the bottom and the unique marking on top. I didn't say anything; I'd abandoned my disc and he'd found it. If he wanted it so bad he was willing to do a complete dye job to eradicate previous signs of ownership, then consider it my gift.
Later on, I saw that same disc again, in the used bin at PIAS. I suspect he threw it into the water and someone else found it and sold it at PIAS. I didn't buy it back; I'd moved on.
As to discs I find, I always will call the number if there is one. Some have said I could keep the disc, some persons were in places like California, Wyoming, Texas, and Tennessee, and said I could keep the discs. Some I arranged to return; they sound grateful their discs were found, and Disc Stalker is good about holding discs for the owner to retrieve them. Some don't call back, like the person whose Groove I found in the middle of the fairway. If they don't call back or if the disc isn't inked, I own another disc...
