The great tribulation will be unprecedented in terms of suffering pain etc.
Yes there is the everyday sorrow that happens because of sin, but I feel like we would KNOW if we have entered this time period. How are people thinking we are already halfway through it?

Just my thinking, things are looking like it could kick off beginning 2013, which would mean the Lord would come back 2020, which seems a fitting year, because of the "clear vision" connotation.
Just a guess of course.
But I honestly feel that such sorrow would be unmatched through any period ever in history.... Ever! And I just don't feel if that is the case....yet. With all the hype of the end of 2012 coming from all angles, I can't help but think Satan has something planned... Of course none greater than the Almighty :)