Lens was DOA as it wouldn't work on my A850. I shipped it back so quickly I didn't write down the serial number, but I believe it started with 1 (saw at a Dyxum database that lenses starting with that serial number are incompatible with Sony cameras). Adding insult to injury, Adorama sent me a ground return shipping label, but I paid for 3 day shipping to get the lens, which I think is pretty lame as I will now have to wait two weeks or more before I get a refund.
Frankly, I'm angry with Adorama about this. They sold me a dud lens that wouldn't work on my camera, a lens they marked as E+ (better than excellent) condition. There should have been a note that the lens wouldn't work on Sony cameras; did they even bother to check the lens on a Sony camera before labeling it an E+ lens? Big thumbs down for Adorama from me as this isn't the first time I've been disappointed by them (the last time I had something shipped ground for "free" from them, it took forever to arrive), I won't use them again.
As for the Sigma 100-300/4 copy I got, I was able to get a couple of shots off with it shooting it wide open with no AF. Tried 200mm and 300mm, and it was pretty bad; tried stopping it down a stop at 200mm by twisting the lens on the mount until the meter showed a stop slower shutter speed, and I still wasn't impressed. Given that, I would probably have sent the lens back anyway. I know a lot of users have praised this lens, so maybe I just got a copy that has poor optics.
Anyway, when the money finally comes back I'm going to try a Tamron 180/3.5 macro; especially since there are no Sigma 100-300/4's to be had. I'm a little on the fence though as the Minolta 200/2.8 looks awfully good, is lighter and faster than the Tamron, and plays well with teleconverters. Still, the Tamron would be the perfect choice for shooting bugs and I would like to get some shots like that with my A850. Besides that, the Tamron currently has a $50 rebate on it, and that helps make it an even bigger bargain.