I can thoroughly recommend a thermarest over a foam mat for a good night's sleep, compact size for strapping to a pack as well as good insulation from the ground. I've used my 3/4 thermarest on rough ground, pine cones, rock, stony beaches, etc and I've never had any rips or punctures. (Mine even survived intact after getting violently thrown around and then crushed in a car accident - in fact if I could get rid of the smell of petrol that leaked onto it it'd be good as new.)
Thermarest mats pack down smaller than foam kip mats too. Mountain Equipment make them too, but they don't pack down quite as small as Thermarest (however they are easier to pack away).
Hope that helps! :biggthump