Just thought I'd relate my first experience with Sigma's service. I've had more than a few experiences with Nikon service and this was a refreshing change. I have a Sigma 150mm f2.8 macro OS lens that is about 2 years old. Doesn't see much use but late last week something went wrong. The inner element behind the aperture became loose and was flopping around inside the lens. I sent it to Ronkonkoma, NY on Friday, they got it Monday. It was back yesterday (Thursday) with a new OS system at NC under warranty even though the warranty card said 1 year (though I thought when I bought it it was a 5 year warranty, just couldn't find anything in writing to back it up). That means they turned it 2 working days. The only gripe is that there has been no communication the entire time, no e-mails to say they had it, that the repair was covered or that it was shipped.
Still, despite the lack of communication, they internet service form was easy to understand and the repair went faster than anything Nikon has ever done, even when they said they would expedite a re-do which ended up taking longer than the initial 2 week repair!
Not sure if this is representative of their service in general, but it was about as pain free as you can get! (wd)