I have to say, I love it! It looks well balanced, it has unique abilities, and the abilities reflect the fluff very well. Finally an archer actually worth playing; certainly much better and more fun than the ranger.
I need a clarification on the concurrence ability and luck rerolls though.Never mind, after rereading it, I realized that the "luck rerolls" of Extra Fortunes are only used for the Destined Arrow ability (right?). It's a bit confusing though, that Extra Fortunes comes before Destined Arrow. Why not just say under Destined Arrow that you have luck rerolls equal to class level / 2?
For Threatening Gaze, it says "the sagittarius can mark a single creature within that she could currently make a ranged attack against." I think you mean "within range that"? And what do you mean by she can make AoOs against that creature but "the foe still does not provoke attacks of opportunity for moving through her threatened squares"? Would every square within range of her attacks count as threatened for the purposes of AoOs against that target? If so, you might be able to get off 5+ AoOs against any moving creature per round with Combat Reflexes and a lot of Dex.
Another thing is that some of the choices for Marksman Ability appear far better than others. Close Combat Shot is nice but useless most of the time as long as you can make 5-foot steps. Maybe also give it the ability to make AoOs using your bow against adjacent enemies? Horizon Eye also seems a fairly underpowered ability since all you'd get is +1/5 to your maximum range for the same range penalty with no effect on anything closer than that. Far Shot is much better, giving you a longer range overall and reducing the penalty for hitting things closer to you.
Patient Hunter is a very situational ability, one that is occasionally useful on the first round of combat to wait for opponents to get within range, but otherwise I don't see too many uses for it, compared with something like Master of Serendipity which just screams Must Have. A bonus to initiative might be an incentive to pick it though. Master Ambusher is not as underpowered as some as them but still seems very situational and limited; maybe merge that with Experienced Sniper? Warning Shot has its uses but I can get the same thing for a +1 enhancement bonus on a magic weapon, and I usually don't bother with feats/class features that I can get from magic items. It should offer something else if you want it to be on par with some of the other abilities.