How long does it take? About a 20-25 minute ride
How often does it come? Its more frequent at night. Every 10-15 minutes or so. We waited longer during the day in between boats than we ever did at night, but found them fairly frequent. Leaving DTD at night, they were one right after the other.
Is it ever full when you try to get on? From POR to DTD, no because that's the first/last stop. I have seen people try to get on at POFQ get turned away due to a full boat because POFQ is the second stop. From DTD heading back, I've had to wait in line through several boats.
Worth it to boat or easier to drive? Depends if you want to hassle with DTD parking and traffic. At night or on a weekend, might as well take the boat and save the stress. If you're in a hurry, drive.