My girlfriend just got from there last week for a medical/dental mission and she loved it. Ulithi is the 4th largest atoll in the world (Kwajalein, Christmas Island-Kiribati being # 1 and 2, don't know #3) and is UNTOUCHED for diving except for the few who dive through Ulithi Adventure Resort. The resort is pricey. Not fancy according to Tahiti or Fiji over-the-lagoon-bungalow standards, but clean, basic rooms that cost a bundle to stay in each night b/c it costs so much to transport building materials to a remote atoll. It sits about 100 miles NE of Yap and is serviced a few times a week through Pacific Missionary Aviation. The service is available to the public, not just missionaries. I'm a pilot and from what I've seen of their planes (2 Raytheon King Airs, multiengine), they're in excellent shape and the main pilot for that route (Peter) is German and has tons of flying experience. I think the max luggage is 50 lbs, including hand carry, and $1/lbs. thereafter.
As for the diving, the sites are wonderful from the photos that my girlfriend took (Oly C-4000/PT-015). Snorkeling just 300 feet off the resort along a wall that drops from 40-400 feet. She said that there's tons of fish, and on one snorkel adventure some large shapes appeared from the deep -- eagle rays that must have been 5 feet wingtip to wingtip, which is quite large for that species.
Only thing to watch out for is the airfills. On the only dive she was able to do, she and her two dive buddies got headaches 10 minutes into the dive. They thought it was b/c the compressor's exhaust empties into the same enclosed room as the tanks are filled, so make sure that isn't the case if you go there. The resort is the only place that has scuba. For that matter it's the only public accomodation in the entire atoll. They were able to get a reduced rate of $20/night, courtesy of the chief b/c of the free medical/dental services, but expect to pay $120+/night normal price. It'll seem steep for what you get, but that's how it is in remote islands with very little shipping/air freight.
The island has about 700 inhabitants, and at a neighboring island the chief has forbidden western clothing and alcohol. The atoll is very sedate, so don't expect a Phuket/Cabo party. Women still go about their daily lives without tops, wearing lava lavas and the men only thus -- both cover their bottom halves only. Walk single file through villages, and don't take photos of people unless you have their permission. There's a fabulous place called Turtle Island where hawksbill turtles go to lay eggs, but there was no gas on the whole atoll when she was there for the motorboats to go out.
Have fun -- you'll be one of the handful of people in the world to experience Ulithi.
