A cross style bike with larger than cross race tires is good for mixed pavement and dirt rides, and dirt roads, but pales in comparison to an actual mountain bike once the trails get technical. Not that you can't do it, it just isn't optimal equipment.
That said, here's my cross bike with 700x42 ritchey speedmaxes. I have since replaced the gossamer cranks with a raceface cadence, changed the chainring from 38t to 42, added a BBG bash guard, and replaced the long cage ultegra derailleur with a short cage.
When more trail and less road is involved I run a panaracer fire cross 700 x 45 on the front.
