I've got 700x32 Marathon Plus on my Specialized Tricross.

They seem to be all but indestructible - I used them on my Rockhopper until one wore out and I replaced it with a Marathon Extreme to get a better tread pattern for use in the mud, and put them on the Tricross after getting a puncture using the stock Borough CX tyres.

They are an absolute pig to put on, and they will make a ride more bumpy as they won't absorb bumps in the road as well as a less protected tyre. That said I shudder to think what it would take to puncture them. I've pulled inch-long thorns out of the MTB tyres that didn't get through and on both bikes feel no need to dodge patches of broken glass in the road (if it's easy enough to avoid I will but if there's traffic about I'm confident the glass won't cause punctures).

If you only ride on tarmac or other mostly smooth surfaces they should be fine, although if a bumpy ride is an issue for you then you might want to look for something with a little less protection from flats. If you want something with a slightly more aggressive tread pattern you could look at the Plus Tour or the Extreme. The Extreme doesn't have the same slug of plastic to protect it, it uses what I think they call a ceramic layer. I've put probably 2000 miles on my Extreme tyre without any problems.