Considering their unreliable low quality warranty service, it's a big pain! My Sig 50 just returned from the third round of calibration from Sigma NY, still not focusing right. Not even close! What are they doing there? It feels like they don't even have a skilled technician and a good equipment there. Or, maybe, they just don't give a ****! Anyway, I'd rather have slightly less perfect but working Nikon lens than a Sigma lemon. Even if you get a good copy and it is working ok. with your current body, there is no guarantee it will work the same with your next one, especially if you going from DX to FX. My Sigma's focusing is significantly different on my D40X and my D700. There are lot of things to consider, when choosing the best 50!Seems like if you get a good sample of the Sig, then you're in the good (and should be, given it is a little more expensive lens, heavier, etc.), but that variety in samples is a pain to deal with.