I heard on Security Now (twit.tv) that they (among other companies) were asked if they ever provided master keys to US law enforcement, and they refused to reply.
As far as I read it they refused to reply to the question about them having handed out masterkeys. They did not reply that they refused to hand out masterkeys.
This sort of denial is hard to read as anything else than that they have already handed over the keys and aren't allowed to talk about it.
It has caused me serious concerns about if I should bother doing a full trial with fastmail, which otherwise seemed like an excellent (although somewhat pricey) replacement for gmail.
You can say it has definitely validated my concerns about fastmail using a US-based hosting provider. If I was fastmail I would be extremely busy looking for a reliable hosting partner elsewhere.
People looking to jump ship from Google are doing it for one of two reasons: 1. Enough with the Google or 2. Enough with the US spying on everything you do.
Stuck with a US datacenter they wont be able to grab near the amount of customers the market is more or less throwing at them right now.
Edit: I work for Opera Software/FastMail.FM
However, even if you indeed handed the keys to the US government, you will be bound by them not to disclose it, so there's no much point answering either "yes" or "no" as long as you or any of your company assets are in the reach of US government.
The same line of thought applies to any company connected with the US in any way, not just to Opera/FastMail.
Anyways, thanks for the update.