As others have pointed out, Silence is a near-perfect counterspell. Just cast it 5 ft. from the wizard and voila! His spell is ruined because he is suddenly in a silenced area. A vast majority of spells require verbal components. And having all my spellcasters take the silent spell feat just because the PCs are wont to use it as a counterspell is not an ideal solution. Consequently, I rule that any creature either targeted by OR in the area of a silence spell may make a Will save to negate. Incidentally, I do the same thing with a magic circle forced upon an unwilling creature.