I used to ride SPDs. I hated them. Float, Platform, Adjustability, Tension all problematic IMHO.

I now have Speedplays X-3s. I like them a lot.

If you want my full opinion on SPDs, do a search for SPDs or Speedplays, you'll find at least a couple of well-reasoned rants under threads concerning both pedals and knee trouble. (Both posted since about 10 June 2002.)

Cheers,
Jamie