I fitted Ice Spiker Pros for the first time at the weekend. They were rubbish in 6 inches of powdery snow, but so was everything else!
Commuted in today and the snow has been compacted/turned to ice, and the tyres were great, once I'd got my head around the fact that I really could ride over black ice without crashing every time. Mind you, my flattish 12 mile commute took an hour and 20 minutes, but that was partly me being a wuss until I got my confidence. On clear tarmac they span up to 16 mph without busting my legs or my lungs.
Didn't know about the bedding in thing, but not noticed any missing spikes yet.