I have and also have friends that have done this. Here are a list of things I can remember that have happened to one or more of the vehicles.
-Carb, the worst problem, fuel evaporated leaving a resin in fuel bowls, jets, lines, filter, and ports. Accelerator pump and power valve diaphram dry rot and deteriorated. Required a disassemble and rebuild.
-Distributor contact areas corroded. Wouldn't rotate properly, (gummed up/corroded?). Replaced.
-Spark plugs, corroded. Replaced.
All of the engines were drained/refilled w/fuel and oil. Then, probably most importantly, the oil pump was primed prior to attempting to start. One other thing I can remember doing to a boat engine was removing the spark plugs and spraying WD-40 into the cylinders (let sit for awhile) and turning engine w/large socket and breaker bar. Good luck