Head-fi is a place where people gather to share and obtain information. First I have to say that not all information here are bad, obviously. However there are a few fundamental flaws that contributes to the bad information flow model. Many are already mentioned.
-Inexperience-
This forum here is a bit different form other audio forums out there. A lot of the people here are (mostly young) people who just got a DAP and want to upgrade their earbuds. The recent smartphone trend also adds to this. Thus the demographic is very different from other speaker oriented hi-fi sites, where they most likely own a property (well, you need a place to house them don't you?), which translates to (in general) an older bunch of people and thus more experienced in audio demographic. We have experienced audiophiles here who have been in the hobby for decades, but they appear to be the minority here.
And being inexperienced in the hobby leads to two things. As they have not heard the really good stuffs, they tend to exaggerate the difference between the low end and the not so high end stuffs. On one end there are people upgrading they equipment to something-better-but-not-that-good kind of equipment (budget DAC to replace decent sound card, one consumer DAP to replace another). On the other end we have people pursuing audio nirvana by going for uber expensive portable setup. Sure they sounded good and different, but in the grand scheme of things they are not that good and different, and no matter how good they get they are still IEMs. There are just more efficient use of money for audio quality. I think this is a significant source of disappointment.
Thus I have come to learn to put more weight seasoned hobbyist who have been around for decades than someone who strap the latest portable amp for latest gazillion drivers custom because they just got an iPhone.
-Emotion-
A good amount of people post are people that are having gear fever. Gear fever is self sustaining. People buy something and get crazy about it and start posting stuffs here. The more they hang out here the more stuffs they buy and the cycle repeats. Gear fever prevents one from objective judgement. This kind of fever is also often contagious. On the other hand people who are genuinely happy and had looked past the equipment tend to disappear from the forum. This leads to the skewing general "consensus".
-Source recording-
I admit that for most of my music, my equipment just sounds ok, even those purported to be "audiophile recording". Only once in a while, I get the "this is it" tracks. Simply put most mainstream music does not benefit beyond mid end equipments. If you have trouble differentiating 128kbps from higher bit rate this is probably why. Back then I could even hear difference between 128, 192, 256 and 320kbps MP3s out of some Creative Soundblaster (the one before Audigy, can't remember the name) with a mere Sony MDR-EX70.
-Lingo-
Because of a combination of inexperience and bad source recording that they are accustomed to, some purport to hear something sounds "natural" or "balanced" when they don't really know how they sounded like. Or when they describe something sounding "real" when they actually meant it sounded exactly like they are in a real rock concert where heavy compression is employed. This is where I put weight into the music genre that they listen to, or the instruments they play.
Personally I am fortunate to have local stores that stock a plethora of headphones and earphones. I have auditioned most of the top of the line IEM and portable amps. Thus I am able to verify all the hypes that are being perpetuated, I believe most people here buying blind will have to rely on return (also much harder to compare side by side). I am also made aware of the inherent limitation of a portable setup and the point of diminishing return sets in pretty early, not to mention the environment that they are used in. In fact I thought all of the multi drivers IEM are objectively inferior to ER-4P (instead of just being different). They all cost much more but the transparency is just not as good (the limitation in miniature crossover?). Although I can see how they can be more fun if one is limited by source material.