I also usually leave things where they are unless there is contact information on the object so I can call the owner. I figure I am doing the owner more of a favor by leaving the object where it was lost, so he can find it.
There is a famous story about some Yeshiva. I think it was Kelm. The story is that someone left an umbrella there and came back 13 years later and it was in the exact spot where he left it. The story is told in order to portray the middos and ehrlichkeit of those who learned in Kelm.