boatgm does. I remember because he has a great boat name. Carabao.
I lived there years ago (the 90s). There wasn't a lot of marinas, yards or used boats back then. Try to get to the military bases. The most boats for sale I found were down in the Sumay marina at Apra Harbor. Might get a deal from a military member leaving island.
I visited Guam last year (spring of 2011) and spent a couple of day driving around seeing some of the sights. I saw very, very few private "yachts" in Apra Harbor. Most of the "recreational" boats were sport fishers and charter operators. My impression was that there were not a big used boat market on the island. It will be interesting to hear about what you find.
I live in Pago Bay. Guam is a hard place to keep a boat. The typhoons are strong and common. I would enjoy showing you around but am on my boat till after Christmas. There is a group of traditional boat builders near the Baseball stadium, they meet on Saturdays and are friendly folks, the Marianas yacht club is also a great place for a meal and some boat talk.
Fun thing to do. Every Saturday, Guam Boonie Stompers offers public hikes to a variety of destinations such as beaches, snorkeling sites, waterfalls, mountains, caves, latte sites, and World War II sites. We meet at 9 a.m. in the center court of Chamorro Village in Hagåtña. The cost is $2 for hikers over 12.