Myths and Misconceptions About Fountain Pens
You hear a goodly number of myths about fountain pens. In my experience, all of the following are untrue. I'll explain.
You need practice to write with a fountain pen
You already know how to write, yes? It's not all that different; keep the shiny side of the nib up and don't press too hard. The only fountain pens that require any training to use are the italic calligraphy pens, which are not intended for general writing.
That being said, it helps a lot if you write properly, just like how they used to teach in school. If you hold your pen in a funny way or picked up other such bad habits, ask your local elementary school teacher about how you are supposed to do it.
Finally, one of the great ergonomic advantages of fountain pens is that they write on contact with zero pressure. You do not need to press down hard to get a clear line; in fact, this is harmful to the pen and it is possible to permanently damage a flexible nib by applying excessive pressure. Write lightly; the pen is supposed to glide effortlessly over the paper.
You must use the manufacturer's ink in the manufacturer's pen
You can use any fountain pen ink in any fountain pen. While it is true that different inks flow differently and have noticably different properties, the claim that each manufacturer specially formulates its ink for optimal performance in its pens is nonsense.
For myself, Waterman ink works in everything. So does Sheaffer, but it is thinner and looks more washed-out.
You should always use fresh ink
As long as there aren't solids or mold floating around, it really doesn't matter. Fifty year old bottles of Sheaffer Skrip ink are often told to be entirely usable. If stored in sealed containers out of sunlight, ink should keep for many years.
I suspect that penmakers tell you this to get you to buy more ink.
Fountain pens leak
A leaky pen is a broken pen and needs to be fixed. Even a ballpoint will leak if it is broken. In working condition, a fountain pen is no more likely to be leaky than any other pen.
It is true that when they do leak it tends to be more spectacular, as the free-flowing liquid ink sprays and soaks into fabric more easily than the paste ink in ballpoints. However, most fountain pen ink washes out cleanly with a good overnight soak in a little detergent. The same is not true for other types of ink.
Fountain pens leak in airplanes
Many will tell you that air travel and fountain pens don't get along. The pressure changes in the cabin causes the air in the pen to expand, pushing out ink and leaving a nasty surprise the next time you uncap the pen. Therefore, you should travel with your pen completely full or completely empty, and to always leave it pointed upright.
I suppose that makes sense and is sound advice, but I don't follow it and have yet to witness any leaking. I've even used fountain pens in-flight to do crosswords or doodle or whatever to pass the time. It seems that most modern pens with comb feeds and large collectors in the section are highly resistant to minor pressure variation. This is aided by the fact that modern aircraft cabins are pressurized.
Heavy pens are higher quality
Writing with a very heavy pen for an extended period of time is quite uncomfortable. In the Days of Yore, when fountain pens were used by everyone, they were usually made of lightweight material for exactly this reason. Now, because luxury pens are power jewelry, used only for signatures, this practical concern isn't a big issue. The silly consumer equates weight with quality for some inexplicable reason, and the customer is always right.
At least many of the top manufacturers still make their top-end pens out of good old-fashioned plastic (MontBlanc, Parker, Aurora, Namiki, Pelikan, etc, all come to mind).
Blotters are necessary accessories
I don't know about you, but I don't make a habit of running my hand over the ink before it has dried. It dries plenty fast by itself. If anything, being careless with a blotter usually makes things worse. While it is true that a heavy feeding broad nib pen can lay down enough ink to make the use of a blotter possible, this generally isn't a problem in medium or fine point "daily user" pens. If it is a problem, use different ink.
I have no idea how lefties avoid getting their hand all over the wet ink, though. My wife is a lefty and does not use fountain pens (despite having access to my collection of hundreds and hundreds) for that reason. She did totally abscond with one of my Parker 21s, though (fortunately, there are a half dozen more from where that came from).
The nib will mold itself to your particular style, so don't let other people use it
If nibs personalized themselves to the user so much as to be a problem for other people, then why do so many vintage pens (which are all second-hand) write great for everyone? As long as the nib is undamaged, the only part that wears is the point, which is tipped with hard metal. Unless you make a habit of writing on sandpaper, it is not going to wear out in your lifetime. If the nib is smooth, it will pretty much stay that way.
If the nib is not smooth, it will become smoother with time as it polishes the iridium repeatedly while writing. Someone who writes rather differently may feel the nib is still a little scratchy as he/she will be polishing a different area. However, if the nib starts out pretty much smooth in all directions (as is typical with modern pens that use large ball tips), you won't notice any changes whether or not you lend it out to people. Vintage nibs are often not so rounded and smooth; this is likely the origin of this myth.
There is one good reason to not loan out your fountain pens: the other person might take a liking to it and walk away with it.
Gold nibs write better than steel
The material used for the nib plays only a very small part in determining the writing quality. It is irrelevant as far as smoothness is concerned, as the only part that touches paper is the tip, which is welded hard metal. It is easier to make a good flexible nib out of 14k gold than either steel or 18k gold, but the geometry of the nib itself is far more important. In modern pens, corrosion resistance (which was the original reason for gold nibs) isn't really an issue.
As far as aesthetics are concerned, gold will always stay nice and shiny, while gold plated steel may eventually lose the plating, which makes it look ugly. Other than that, there really isn't any practical difference.
You can squirt your friends with them
With the exception of the Sheaffer Snorkel pens, fountain pens pretty much just squirt you. The ink doesn't have a clear path out through the feed, so it just kind of dribbles out vigorously. And what a mess that is to clean up!
The Snorkels, however, are basically water guns when it comes to squirting people. Very cool.
The collector's market is hot, and pens are a great investment
No they're not. While there is the occasional pen that sells for a ridiculous sum at auction, the vast majority simply don't appreciate in value. If you look at prices for older pens, they only go for a fraction of their inflation-adjusted prices. It is a little early to tell for the modern phenomenon of "Limited Edition" collectible pens, but you will see that their prices do not rise significantly over time either. In short, your expected return is negative.
If you want an investment, look to the stock market. Pens are for writing and for fun.