I have a pair of shimano m540 spds that have been on my commuter for 5 years. Never greased or attended to other than a qick squirt of gt40 over the surface every now and then and a wipe down with a rag.
Still work as well as new, bearings smooth, clip in and out faultless.
They get an average of 150km a week, i think that is a remarkable feat for something that gets punished as much as a pair of pedals under my bulk!
Hurrah for stuff that just works!