I don't have spacers on the front. The main reason I added spacers to the back, was to "even out" the tires in the fender wells so the back looked the same as the front. I don't know if you can tell from this picture, but they are pretty close. Plus, I do like the wider stance.
<img src="http://www.zjstech.net/~library/3497/P7030006.JPG">
Be sure you get spacers that are made to be used with load-centric lug nuts. Load-centric nuts are tapered so they will center themselves into a tapered hole in the spacer. The nuts should be included with the spacers, and have 1/2"x20 threads to match the hub studs. Also, try to get spacers with studs that have the same thread pitch as the hub studs if you can. There's nothing wrong with metric studs, except that you'll have to buy a whole new set of metric wheel lugs to go with them. This picture shows 2" spacers with load-centric nuts.
<img src="http://www.zjstech.net/~library/3497/Wheel%20Spacers-2in.JPG">
Other things to consider: If you get aluminum spacers (which most of them are) the torque used on the lug nuts probably shouldn't exceed 95lbs. Ford recommends 100ft/lbs of torque on the stock wheels. What I'm getting at is, you don't want a shop mechanic torquing down on your aluminum spacers, with his air wrench, and breaking them. Some shops won't even touch wheels mounted on spacers, due to liability concerns (NTB for example). Bottom line - be prepared to do your own tire rotations from now on, so you'll know the correct torque is used.
Also, you know how you're supposed to check and re-torque the wheel nuts after 25-50 miles following a wheel install? Well, you'll need to check and re-torque the nuts holding the spacers on the hubs the same way. This means taking off the wheels again to check the torque on the spacers, but it's a good thing to do. Once you're sure the spacer nuts are set, then you can check and re-torque the wheels afterward. I also test the torque on the spacer nuts every time I rotate the tires (every 5,000 miles).
Good luck, and post pictures after you install your spacers.