Much has been said, but a few responses:
Haven:
one place metal shows it's worth is in trade goods.
It's not like there's any shortage of trade goods. Personally, by my second year I'm generally throwing ten to fifteen thousand worth of profit at traders just to clear my hallways of junk stone.
Kagus:
You *will* need magma.
...pretty much, yes. It's not totally unrealistic to smelt ore and make metal items on a heavily forested map, but it seems like the biggest source of metal for most players is the goblins. And it's not practical to use wood fuel to melt down items. It takes way too much fuel.
So you pretty much do need magma to have any meaningful metal industry, and you need to wait for goblins. The problems being that:
1) Magma is something you absolutely need to do on purpose. I've never seen magma on a map unless I specifically went looking for it. Personally I tend to NOT do this, because maps with magma tend to be low FPS maps.
2) It takes YEARS for the goblins to show up in large numbers. So even if you do have magma, it takes years before you can start serious metal production, before you can start serious training your weapon and armor smiths...by which time you probably already have several legendary, or near-legendary crafters of every other profession you care about. Why bother start up a metal industry, why bother starting to train a weapon and armor smith from low level...when you already have a legendary leatherworker, mason, carpenter, etc?
Kagus:
A wood-based fortress is easier to get up and running, but will be difficult to sustain
...whatever extent it's more difficult to maintain a wood-based fortress is pretty much trivial. For lots of reasons. "Heavily forested" maps are easier to find that maps with lots of metal, and you can get them gaunrunteed when you choose your starting location, as opposed to metal ores, which are random, and even if you choose a likely place for metal, what you actually get isn't certain. Also, trees grow back...so you can never run out, unlike metal, which does run out. And, while I've never played a game long enough to have it happen myself, I've read that eventually the goblin sieges STOP. What must that be like? Dedicating so many years of a game to a metal industry and then one day Poof! it just dries up and dies? Meanwhile, all your wood and glass procurement methods continue on into perpetuity.
Also, because of the quantities involved it's very easy to get wood from trade, whereas it really isn't practcial to get metal from trade. Traders are perfectly happy to bring LOTS of wood, whereas no matter how important you tell them metal is, they never seem to bring more than a few bars at a time.
Finally, if you trade in that anvil because you're never going to use it, you can use the 1000 points to bring in an extra 300 logs with you. That's enough to supply all your dwarves with beds for the entire lifetime of the fortress, and build 100 barrels. Between that and trade, you don't even need to chop down trees. If you don't bring axes, that's another 200 logs you could bring if you really wanted. That's enough wood to run a thoroughly wood-based fortress for years without ever cutting trees or trading for wood. Add in trade, and it's completely trivial to run a thoroughly wood based fortress on a woodless map simply by bringing logs with you and trading for more when the caravans come.
How much metal do you generally bring? Maybe...five bars?
Dadamh
if you are talking about obsidian, then you have magma
Not neccessarily. Obsidian occurs naturally. It's not difficult to find entire z-levels made of obsidian. Sure, if you want that, you need to look for it when you choose your starting location, but in my experience it's easier to find obsidian layers than to find magma. And, obsidian layers can be found in flat, small, high-FPS maps, unlike magma, which often means low-FPS mountain maps.
Quiller
I guess the point is
My point was exactly what the post title says. Metaless fortresses are a good thing. Not just "acceptable," but GOOD. It's actually BETTER to not bother with metal.
* Having a practical metal industry requires more concessions in your starting location than any other type of industry
* It's easier, cheaper, and more practical to start, as well as to maintain any industry OTHER than metal
* Even once you get it started...metal industry isn't much better than anything else. Armor is the only thing that metal IS better for...but because of the skill training, it takes YEARS for metal armor to significantly pass leather.
* Metal industry requires more dwarves dedicated to more skills than anything else. Wood burner, furnace operator, armorsmith, weaponsmith, etc. Meanwhile, most of the alternatives that replace a metal industry are all dwarven skills that you have anyway. Whether or not you have a metal industry, you have definitely have a carpenter, a mason, etc. Making wooden or stone traps uses skills that every fortress always has no matter what. Metal traps requires a specialized dwarf training a skill that you wouldn't otherwise use. Making stone swords uses a skill that every fortress always has no matter what. Making wooden sheilds uses a skill that every fortress always has. Again...metal...requires massive specialization.
* It's massively easier to train relevant skill for everything other than metal skills
* By the time you can start training metal skills, you probably already have legendary crafters for everything else. Yes, metal armor crafted by a legendary armorsmith absorbs more than twice as much damage as leather armor crafted by a legendary leatherworker. But the amount of time, effort and expenditure it takes to make a legendary armorsmith is impractically ridiculous. I've been playing since 2d, and I've never had one. Ever. I don't think I've ever made it halfway even in games that I started with a Proficient one.
* Even once you get it going, the benefits of a metal industry aren't that great. If I need to already be able to break a goblin siege to get my metal industry going...what do I need the metal for? Metal industry is basically just a timesink.
Metal is seriously gimped. It's certainly much EASIER to not bother...but even if you do, the benefits just aren't that great. If you spend the time and energy that it takes to get a metal industry basically functional on something else...you'll generally be better off for it.
The only people who are benefitting from more than very casual metal industries are people who are using reveal utilities to cheat and find magma within the first few hours of playing a map.
If you have to use third party utilities to benefit from metal...again, I think it's safe to say that it's fairly well gimped.