I'll pop in here with some personal experience. I have been using a Nikon 8000 for the last 4 years, and it is a fine scanner. I agree with the other posters that the glass carrier is a necessity, and the liquid mount carrier is another beneficial step beyond that for this scanner.
But recently, I got the opportunity to pick up a just-overhauled Howtek HR8000 drum scanner for a very good price. I bit the bullet and bought the DPL pro scanner software to drive it, along with a mounting station and supplies.
I had previously wet mounted my negatives on the Nikon 8000, so I understood the basic idea behind wet mounting. I downloaded the excellent mounting video from the Aztek website, and after a few sort of pathetic first attempts, I got the hang of mounting the negatives on the drum. Total time invested: about 2 hours.
I mounted the drum and went through the process of learning how the software works. It is both very simple and very powerful. I made some scans, and I must say that while I was very satisfied with the Nikon scans, after seeing the drum scans, their quality simply blew away the Nikon's. There is no doubt that the resolution and ability to resolve detail in dense areas of the negative is superior to the Nikon. This should really be no surprise, since the resolution of the Howtek is 8000 spi versus the nominal 4000 spi of the Nikon 8000 (in practice, the Nikon 8000 has more like 3000 spi effective resolution).
Is it more of a pain in the ass to use? Sure, it takes more time than simply throwing a negative in the Nikon 8000 to see what I have. But here is the cool part: you can load up a pile of smaller negatives on the drum scanner, tweak each negative for dynamic range, contrast, and scanning resolution, and then set up a batch job, and then leave it alone for a few hours. When you come back, you will have a computer full of really good scans. This ability to batch up a bunch of negatives and then let the scanner run unattended is a huge time saver. With the Nikon, if you decide to carefully scan a dozen 6x9 negatives, you better be prepared to sit in front of your computer for a while. The tradeoff with the drum scanner is at the front end of the process, where it is a little more time consuming.
Just my 2 cents.