Do people trust StartCom? Just curious ... I always wondered why you have all these very expensive cert providers who charge a lot for SSL certs, and then this mysterious company with ties to Israel is handing them out for free? I know it's pure paranoia, but this would seem to be an excellent way to compromise a lot of SSL traffic if you were into that, and the Israelis are pretty famous for all kinds of spying acti…
There are about 100 root CAs, and something like 1000 CAs if you include intermediates (controlled by ~650 different organizations - https://www.eff.org/observatory), and browsers trust ALL of them. All it takes is one to issue a malicious cert, or to get hacked, to do a MITM attack on ANY domain without showing a browser warning.
The trustworthyness of a single CA doesn't make a difference, because if any CA isn't trustworthy then an attacker can use them instead the other ones. This is the problem with CAs, and the problem with centralized trust systems in general. There are hundreds of weak points.
But also, StartSSL does fairly thorough identity verification. I've had to send them photos of my passport and talk to them on the phone to do identity verification. It's also worth noting that it's the CA that both https://www.eff.org/ and https://pressfreedomfoundation.org/ use.
As long as there's a broken CA system, the choice of CA does not matter in the slightest as long as it's trusted by browsers. Users only care if it breaks a website with a scary warning, but if it doesn't, it doesn't matter. There's no need to spend money.
StartSSL does charge if you have more than very basic needs, like if you want multiple alt names, or if you want a wildcard. But it's still cheaper than the competition.