In the Star Trek novel "Yesterday's Son", Spock discovers that he fathered a son with Zarabeth when he was stranded in the past in the 'All our yesterdays' episode. So a male hybrid produced by a Vulcan male / Human female can be fertile with humans.

http://en.memory-alpha.org/wiki/Yesterday%27s_Son

Can hybrid Vulcan/Humans procreate, or are they like mules?
In TNG and DS9, we often see the use of shuttles and runabouts. What is the deciding factor of which one to use? How come we only see one use of a runabout in TNG? Is it only about the crew size on board? Yet shuttles have been shown to carry quite a number of people too? Is it speed?
