So, while we're on the subject of how snipers can harass the enemy's offensive players, can we add some good counters people have found effective? As I've said before, I make a point of going after offensive snipers (though after this discussion it will be more for tactical reasons than "I hate osnipers"), but there are some, like Shaska, who are good shots and good duelers to boot and are able to kill me before I'm close enough to be effective (such as it is).
With weak duelers, I find it's enough to just camp their favorite spot. Tends to make the sniper whine, I've noticed. But with those that can knock you out of the air with CG in a couple seconds, like Lillith, it's a little more difficult. For me, I try to consider it enough that I can distract them from sniping, sometimes to the point that I don't even go for the kill; I just shoot em, dodge their shots, hide, and wait for them to try to snipe again so I can rinse, repeat.