I use plastic platforms on my single speed. It's my get on and go bike so I like to just wear whatever I have on atm. Even when I take it out on planned longer rides, I still like the platforms on it. Now, I also use clipless pedals (have been since they first came out yeaaars ago - which my first pair were some real crappy Onza clipless jobbies that once you were in you couldn't get out) on both my geared road and mtb bikes. The power transfer is what clipless are all about, IMO. However, I much prefer bmx type platforms on my single speed for their simplicity. Alot of riders like skate style shoes with them, but I like indoor soccer shoes.

LessonLearned - there are quite a few low weight, higher quality alloy platforms out there - some of them well over $100 a pair. The plastic platforms work just fine (I have the Hamilton Animals poly and like them well enough), but if platforms are your thing and you want to get a "nice" pair, look up some of the alloy options.