I just made a phone call and within 15 minutes I am talking to an authorized Herman Miller warranty center up in Tampa.
They should have a new seat in a few weeks and will even do the work replacing it. No grief and the people I spoke to were very nice.
...
So yeah, I am pretty happy about all that.
I just bought an Herman Miller from an authorized dealer (I confirmed yesterday). Got a cool rebate on it and it's going in my "before-taxes expenses" (whatever that is called in english ; )
I decided to buy a new one to get the 12-years warranty (non-transferrable as someone here on GH pointed out to me).
Now that I see your post I certainly don't regret it. I went for the older Aeron: I hesitated with the Mira but then when I was in the U.S. I was in love with my Aeron so... Bought one in Europe now
Sure it may seem a bit expensive to some for "just a chair" but I don't care much: used ones are also very expensive, so I should always be able to sell mine in a few years for a good price if needed.