What are the biggest problems with a neglected boat?

my friend and I like to fish. we have found an abandoned boat in my friends neighbors yard. he is renting the property. nobody wants the boat and we are in the process now of legally obtaining the boat. It has been sitting there for about a year and a half with trash piled on it. the outboard motor looks pretty new and the boat is a 15 foot - fibergl, vee bottom hull with a windshield. we dont know much about boats so other than changing the oil and cleaning the thing up, we dont know what problems to check for. does anybody know the top things that would go wrong on a neglected boat?