If you attend the entire New Bedford Moby-Dick marathon and don't nap at any point, you will be awake for at least 25 hours. (In reality, you will be awake longer than that, because you will have been up for at least an hour or two before the marathon starts and will remain up another hour or two after it ends.) Since the marathon ends in the middle of the day, your inclination might be to drive home as soon as it's over. But that's probably not a good idea, unless you have a very short drive.
The fine folks at "Mythbusters" demonstrated the effects of sleep deprivation on driving in a recent episode of the show. (Specifically, it was episode #153, which originally aired on Nov. 3, 2010.) Two of the younger members of the crew, Kari and Tory, tested the claim that driving while sleep deprived is more dangerous than driving while tipsy. A driving course was laid out, including both a complicated "city" portion and a monotonous "highway" portion. Then Kari and Tory drank enough to raise their blood alcohol level to just below the legal limit in California. Each of them drove the course, and their errors were recorded.
For the sleep-deprivation part of the experiment, Kari and Tory stayed awake for 30 hours, which, as it happens, matches pretty well the experience of staying awake for an entire Moby-Dick marathon. They then drove the same course. On the "highway" portion, both of them did much worse than they had while tipsy, making more than twice as many recorded mistakes. On the "city" portion, Tory also did a good deal worse while sleep deprived (Kari was actually a tiny bit better tired than tipsy).
Now, one important difference between Kari and Tory's sleep-deprivation experience and that of most marathoners is that Kari and Tory were not permitted any caffeine or sugar during their period without sleep. Most Moby-Dick marathoners get plenty of caffeine, and sugar is also much in evidence. But I wouldn't rely on that to get me home safely.
My recommendation is that if you're going to stay for the whole marathon, you plan to spend Sunday night in New Bedford. That way, you can enjoy a leisurely afternoon and dinner following the marathon, and a good night's rest before facing the drive home.