My S.O. has been running Marathon Plus (700x38) tires on her hybrid for the last year, with no flats so far.

The ride is a little odd. It has a slightly "cushioned" road feel, but she got used to it quickly. The only drawback I can see is that it's a HEAVY tire, especially in the larger sizes like 38mm. That probably doesn't matter on the type of bike it's likely to be used on -- commuters, town bikes, touring bikes, etc.