After having read page after page of people describing the game in five words or less, I've decided to write a bit of a guide for this to help the new folks out. Be aware that this guide may become outdated and/or flat out obsolete.
Starting out:
First, don't bother going and fighting to get a bigger ship. Almost everyone on the high seas either travels in a group, or simply has a much bigger ship then you, and you'll probably get sunk real fast.
Instead, head for Moonstyn, and buy as much Vanilla as you can. Leave the port, and sail southeast till you hit Aalbarg. Sell the Vanilla, buy perfume. Sail back to Moonstyn, sell the perfume, buy Vanilla. Keep buying and selling in these two ports, buying food as necessary for your crew.
The more times you trade between these cities, the more money you will have. Very soon, you'll be able to completly fill your cargo hold with either the perfume, or the vanilla before you sail to the other city and sell, increasing your profits per leg even further.
When you are ready to buy a new ship, make sure you have at LEAST 20,000 MORE then the cost of the ship you plan on buying BEFORE you sell your current one. Then, buy the new ship, hire on your maximum complement of crew, resupply on food, and buy as many cannons and cannonballs as you can carry. Then, go back to trading between the two cities, buying and selling as normal to rebuild your cash reserves.
Main Quest: Okay...this thing has a few bugs unfortunatly. First, let me deal with them.
Bug #1: If the main quest storyline has you trying to find the dark crystal, start a new game. NO-ONE has yet to find the crystal, and there doesn't seem to be a map for it anywhere, though there is a rumor that the crystal can be found on a desert island. (Screenshot please anyone?)
Bug #2: It seems that the main quest bugs if you save and reload your game while your still hunting for the main quest item, making you hunt for the Dark Crystal instead of whatever you were initially asked to find. if this happens, your pretty much out of luck it seems.
(Possible) Bug #3: It SEEMS (though I can't confirm this) that your supposed to run into someone while hunting for the main quest item who tells you who you are and/or helps you find the main quest item. Because I go straight for the location of the main quest item (thus avoiding Bug #2) I never run into this guy. As a result, it may bug the game out, but again, I can't confirm this one way or the other.
Okay, on to the other items:
Treasure Maps: These are found COMPLETLY AT RANDOM by talking to people in Taverns and buying them for 2,000 gold. When you arrive in a town, the tavern is randomized and people there may or may not have a map. To reset the tavern and try again, sail out of the city, and then sail back in.
FINDING a treasure is a little tricky. Once you have the treasure map, compare it to your global map, and then what your seeing on screen as your sailing around. When you can match the map to what you see on screen, sail to the X, and beach the boat DIRECTLY onto it by sailing into land. Then hit "L" to land and then choose to search. If you landed exactly on the X, you should find the treasure. If not, sail a little bit to either side and try again. If you still can't find it, make sure your in the right place (compare landmarks, trees, rocks, mountains etc.)
The Global Map: This seems to be a complaint for a lot of folks. As far as I can tell, the map doesn't give you the listing of cities in alphabetical order. Instead, it goes from the city in the top left (northwest) part of the map, and goes to the right (eastward) all the way across the map, and essentially circles the map, hitting each town in order.
Combat: Oh boy. First things first: The gunners on your ship arn't the brightest. Instead of using spacebar to fire, use Z or X. Each one controls ONE side of your ship, letting you fire in just the direction you want.
Anyway, I can't think of anything else at the moment. If someone can find the Dark Crystal and post a screenshot of it, that'd be extremely helpful. Aside from that, I hope this guide is helpful.
UPDATE: I received a Treasure Map for the Dark Crystal from one of the people in the tavern. To stave off any questions of "Where!?" please read the above paragraph about treasure maps. In any event, I can now tenatively confirm that the Dark Crystal is a bugged item, because the map I was given pointed me directly at the location of the Banland Stone, and when I picked it up, the treasure map received the little green checkmark, indicating that its treasure had been found. So, that said, the treasure for the Dark Crystal seems to be bugged for certain. If there's a workaround or fix in the works on this I don't know. But at least now we know it's definitly bugged.