I just found out this amazing series thanks to gamedev.net dailies.
Designing a Magic System by Andrew Doull
(Plus a fine article from Craig Perko - found in the series above)
Seeing how magic and its systems have gotten a formal definition over time is both entertaining and enlightening. I used to design a pen and paper RPG rules for fun when I was in my teens. The act of balancing, adding to or removing from a specific rule set is not as straightforward as it might seem. Actually, while I'm all for coming up with cool ideas about magic and so on, I must admit players (including me) are used to defined schemes. So, I guess, we're not just balancing fireballs versus shields, but also marketability versus innovation.
And makes me wonder if we will eventually get used to "common" magic...