I've been running a fast and dirty d20 Modern version. I just scrapped their magic system entirely and boiled it down to a couple of base components.
There are spells, there are circles, there are focii and implements, there are shields. Everything has five levels or so that just climbs in output, area, target numbers, buff or whatever number, or what have you. You make a concentration check to see if you can. You make an appropriate attack or skill roll if you need to. You tell the GM EXACTLY (and that's a necessary stress) what you wanna do. The GM says you can or you can't (and that's another necessary mention since it's REAL fast and dirty). A quick discussion isn't bad, in fact since it's just you GM playing by the skin of their teeth, is sometimes necessary, but keep it quick so you don't spend all night on it.
Bear in mind, this is JUST to tide us over until the game comes out. We all know I'm not a game designer, and they're just happy to have a Dresden game of any kind. The rest of the stuff is covered quite well by the d20 system.