Have Schwalbe Marathons on my bike now too - so far 8 weeks and no punctures after averaging about 1 a month! Excellent tyres - just watch the cornering to start off with. I notice a difference in grip when I lean the bike to far (don't know if anyone else notices this?).
I used to use M+'s but changed to Conti GP4 Seasons, far superior grip especially in the rain, not a harsh ride like the M+'s and 4 Conti's weigh less than 1 M+. I tried the M+'s again after 9 months on the Conti's and it was an awful exeprience and within a few days I gave up the M+'s. I would rather risk the odd puncture than having to ride on such dreadful tyres, in my opinion.