Don't be sucked into buying an item (a pen or anything else) just because the manufacturer has labelled it as "green." If the environment is that important to you (and I hope it is!), think carefully before you buy and remember that the old fountain pen and ink may still be the best option.
Like Heather, I'll ask you to excuse me if this post likewise turns into a bit of a rant.
Let's start with this: I do not use fountain pens because they are eco-friendly, and I do not know if they are or not. What bothers me is blind acceptance of "green" claims.
Here's the problem: nobody thinks about trade-offs. There are trade-offs for everything. Everything. Ev... er...y...thing. (Including the options Heather advocates.) That's what engineering is about, folks. Compromise. I may have barely passed in my electrical engineering major, but I learned that much.
Let's say an engineer is trying to build a better widget by giving it more tensile strength. No engineer can just think, "How do I design more tensile strength into this widget?" Instead the engineer has to ask, "How do I design more tensile strength into this widget without unacceptably increasing manufacturing costs, reducing other good qualities, or introducing or increasing bad ones?" Maybe you can increase tensile strength quite easily, but at exorbitant cost in money or at the cost of losing flexibility, which you also need, or at the cost of increasing undesirable qualities like size, weight, or susceptibility to corrosion.
Trade-offs. If we didn't have them, we could design a perpetual motion machine.
So, let's take a closer look at the eco-friendliness of fountain pens.
Re-usable. Re-fillable. Non-disposable. (I guess those are all the same thing.) I think that's about it.
Water. You need water to flush them between inks. With some pens (I'm thinking piston fillers), quite a bit of water. And I live in California, so huge amounts of energy are used to get that water to me.
Metal. Famously anti-green mining activity was required to make at least part of each of my pens. Even if the barrel isn't brass, that steel or gold nib didn't just pop up out of a dispenser. In fact, if it's steel, it required a steel plant to form the steel after the iron was mined. And if your barrel is brass, then odds are the copper for it came from an open-pit mine, a huge scar in the earth.
Plastic. Use cartridges or a plastic converter? There's a 99% chance the plastic was synthesized from oil.
Multiplicity. Lots of fountain pen users like to collect them. Real eco-friendliness would mean owning one pen. Count me among those who own several and will buy more. (On the other hand, this desire to acquire and own is the same thing that keeps us from throwing them out, so that's good.)
I'm not saying that fountain pens are NOT eco-friendly. I have no idea whether they are or not. I'm just saying we shouldn't assume they're eco-friendly just because they're refillable.
In fact, I'd love to hear from others about any eco-friendly facts I missed.