Typically, the three magic forms rate like this in popularity:
1) pact magic
2) shadow magic
3) truename magic
I'm gonna go out on a limb here and say that the reason for this is because pact magic seems like it is the most powerful and truename magic seems like it is the least powerful. I believe the reason for this perception is because pact magic gives your character a lot of static bonuses that your character can "walk around with," much like the cleric can walk around with hour/level and 10 min/level effects like freedom of movement, death ward, magic vestment, greater magic weapon, etc. The more effects you can pile onto your character the higher the perceived effectiveness.
Shadow magic on the other hand is utility magic. The shadowcaster doesn't "cast the spells that makes the peoples fall down." He casts spells that immobilize or hinder enemies and overcome trials. In that respect he is like an enchanter or illusionist specialist wizard who has prohibited evocation and necromancy. Not a lot of death happening, but a remarkably useful character. He has a lot of tricks up his sleeve that make otherwise challenging situations a piece of cake. For that reason, he is well-liked.
The truenamer is the red-headed step-child of the bunch because of that ever so touchy subject of the DCs that scale with CR. This means that a truenamer's spells are always going to be challenging to cast unless he is casting them on low-CR opponents. The truenamer is every bit as powerful as the others, however, his magic is not as constant/long-lasting as the binder's and not as reliable as the shadowcaster's. D&D gamers (especially 3e gamers) by and large (i.e. most, but not all, so don't accuse me of applying this to everyone) like effects that are simple, reliable, and effective. That is why magic missile is perhaps the most popular spell in the game. There is no save, and force effects can damage anyone. Many of the truenamer's spells are typically simple and VERY effective. But they are not reliable, because there is virtually no way a truenamer can ever have his truespeak skill high enough to succeed on a truespeak check without the chance of failure. Strategic thinkers, like many gamers are, do not like this aspect of unreliability. Many of them probably dream of '1' filled nights where they never get a spell off because they can't roll worth a damn.
Perhaps I'm totally off the mark here. Perhaps not. Given the complaints I have heard and the directions they point, I think I am at least pretty close to the reasons for why people don't like truename magic in general. However, the bottom line is that truename magic is balanced by this random factor. If it weren't for that factor, then truename magic would be way too powerful. Wizards have to budget their spells for the day. Truenamers have no such limit (though the laws of resistance can make things cumbersome). But they aren't as reliable as wizards. That is not a bad thing though. It simply adds an element of randomness into the game and that doesn't mean it is less fun unless the only reason you play the game is to "win."
Anyway, that's all I really have to say on the matter. I'll try to abstain from saying more as it would probably be simply a regurgitation of my points here.
