When you own a luxury motor yacht or superyacht (and what's the difference? I hear you ask: answer in a minute) you really do live in the lap of luxury. With a top deck swimming pool, state of the art kitchen, private cinema, and toys that you can play with such as jet skis and a small motor boat to explore the coves inshore, there is not a lot to beat it. Not only that, you can up-anchor and travel to anywhere in the world that you want to go, safe in the knowledge that your skipper and crew will take care of you wherever that may be.
To answer your question, luxury motor yachts become superyachts at a length of 79 feet, and some of them go up to 200 or 300 feet. Mind you, even at 78 feet that is a fair-sized boat and you can incorporate a lot of things aboard it. About the only thing you won't be able to do is to accommodate as many guests as a larger boat, so you will probably be restricted to six or eight on luxury motor yachts of that size or smaller, whereas with a superyacht you might be able to accommodate 30 or 40. That is really a floating palace.
The average value of a superyacht is $10 million and according to one figure there are 4,476 people around the world who own one, with the top country for owners being the US with 33% of them (who would have guessed?) and the UK is actually in second place with 11%, believe it or not. Those are followed by Italy (5%), Australia (4%) and Russia (3%). Typically, it can take anywhere from 12 months to 3 years to build a superyacht, so the sooner you place your order the better.
Whether you are at the level where you can afford to look at superyachts or "only" luxury motor yachts, the challenge in the used market is finding the right one. Unless you really know what you are doing, you will need someone who is highly knowledgeable to help you, so you need to enlist the services of a reputable agent.