Yes, speedplay rocks! I had the same problem. Check this website:
http://www.epdoc.com/mvv/speedplay/index.html

The outside of the pedal gets worn out and your foot rocks from side to side. Also there is a tremendous amount of float I could not get rid of. I would tighten both float screws the most I could and my feet would still float all over the place. I hated speedplays. I bought spd-sl 105s and they are much better. My knees are much happier.

If you could adjust the float to less than 5 degrees and the pedal wouldn't get worn out it would be a good peddle.