I don't have the cash to buy so I speak in the hypothetical, but if I was sitting here with 100k in my pocket and faced with the decision on whether to invest it and leverage the boat, or just pay cash with the boat I think that my decision would remain to invest the money and use someone else's money for the boat. My equity Line is UNDER 4% right now and you get a third of that back at Tax Time. As far as I am concerned that is REAL cheap money, hence the reason my boat and all 4 cars are on it.
I sleep great at night - but since I'm young I would like to reserve the right to revisit this post in 10 years when my situation has changed and be able to pull the "I was young and stupid" card!!!