I found this article through Tor.com, but I’ll link to the original on N. K. Jemisin’s own site here. It’s a superb argument against the dogmatic need for a magic ‘system’ in fantasy worlds – well worth a read.
I couldn’t agree with her more. My favourite fantasy of all time is Steven Erikson’s Malazan books, and the magic in that is absolutely batshit insane – almost every race has their own particular kind of magic, and they clash in utterly unpredictable ways, any of which might end up destroying the surrounding area (or entire world in some cases). Which means when there’s a conflict every forty pages you can rarely guess how it’s going to pan out. Who wins in a fight between a Jaghut and a T’lan Imass? (No-one, basically, but that’s another story.)
I should really get around to reading Jemisin’s The Hundred Thousand Kingdoms soon, as well. And how good is this cover?!
DAN HARRIS: 10% SCI, 90% FI 
Yeah, many times, the magic systems in fantasy books are WAAAAY overthought, but I like it when there’s at least some sort of rule system with it of some sort, some kind of defined limitations. When there isn’t, those books tend to have way too much Dues Ex Machina for my tastes and I end up rolling my eyes and going, “Oh, wow. You couldn’t come up with another way of solving this? You had to have magical magic come in and fix it?” Or worse, the magic is so powerful, so unrestricted, that I come to wonder why it’s NOT the answer to everything because, hey, magic can do anything in this world. I like it when a system is thought out enough that it makes sense in-story and has at least a little bit of pattern to it, doesn’t get in the way of the characters and plot, but has just enough restrictions that it doesn’t become the answer to every problem the characters face. It’s some of the reason why I’ve been avoiding overtly magical fantasy lately. It just gets to the point where it either has way too much scientific background or not enough believable restrictions, and it’s hard to me to keep believing in it.
Damn, that’s a lovely cover. I haven’t seen this book/heard about it yet. I’ll have to take a look at it.
You’re absolutely right – it’s always pretty clear when the author’s just throwing it in as a lazy plot device, and that’s annoying. I need to be careful for similar reasons though; it’s just as easy in SF to think to yourself: “How will my character get out of this? I know! SCIENCE!”