In reply to Tom the tall:
I'm using Conti GP4 Seasons in 700x25 too. They feel great on rough roads and don't slip about like the show-room tyres they replaced but, as far as puncture resistance is concerned, I am NOT impressed.
It does seem that automotive glass is designed to shatter into a particular size of fragment, however, and those fragments seem to go straight through just about everything...
... and always in the rain while you're slogging through some dingy British town. Why can't the punctures wait for those balmy days and quiet roads when there's nothing but sheep and fields for miles around?