Dude you are definately getting ripped off from that place, don't trust places that pull that shit. B&H has that same lens for $409.95 and there's a $15 rebate on it. www.bhphotovideo.com
What was the name of that place that is trying to screw you? Cancel that order if you still can! I don't represent B&H in any way, I just buy all my shit through them because they're trustworthy and have the best prices from someone I can trust.
To the first guy, it seems like a decent enough lens for what you'll pay, and I think the image stabilizer is definately useful for moving subjects because I think you can switch between both horizontal/vertical IS to just vertical IS for panning and shit. Good luck.
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