Okay, I'm sorry but I must step in.
Unless your pedals are set up perfetly, you will probably injure yourself. I ran fixed cleats on my track bike because I liked the feel of sprinting full out and having my feel locked into place. It also made sense because my q-factor on my cranks was very narrow. I also ran some fixed cleats on my road bike, it felt more stable, but I did end up hurting my knee a bit because the cleat was not adjusted perfectly.
It is true if you had it set up perfectly and your body did not move from your pedal you'd be fine. However, the lateral deviation of everything below your hip does change angle because the cranks move in circles.
Also, standing up and sprinting/climbing increases the need for rotation of the foot because you will be moving the bike left and right and leaning the opposite way. Your foot will compensate with inversion and eversion, but your knees will compensate with the rest of the lateral rotation needed. This works fine on a track bike because standing time is limited, and the tecnique used with stiffer bike and higher speed sprinting is to keep the bike parallel to the ground. But for a road bike it's not so great.
The other reason you should not run fixed cleats is because of the extra tension you will need to run your pedals at. Because you have no room to move laterally, if you accidently twist a bit it'll pop out of the pedal. Tightening up the pedal release is no problem for the seasoned rider, but you may not like the extra force needed to get in and out of your pedals. Though after time you may prefer a tighter setting.
I have also never heard of a stroke being inefficiant because of float. None of the seasoned racers have ever brought it up. I believe it's more of a preference thing.
Here is a good description of the rotation of the lower part of the leg. (comment 5)
http://forums.roadbikereview.com/coaching/pros-fixed-cleats-279039.html
I am of course open to discussion on the power transfer and likelyhood of injury with fixed cleats, but I will not advocate a new rider with underdeveloped cycling muscles to ride with fixed cleats ever.
Maurice