This is an old topic I know, but I stumbled across this by accident, and I thought I'd try and help settle the matter.
Firstly, companies tend to be pronounced world wide as they are pronounced by the people who created it. CZ is an American company (I think) so therefore world wide it should technically be See Zee.
However the British pronunciation would indeed by See Zed, discounting the above material.
As for those who believe they pronounce it correctly as See Zee due to the fact that it is American, and that is how it is supposed to be pronounced, while fair to say, that is correct in American English, however it is only the case in American English. The rest of the world does speak British English (for the most part) where it would be Zed. For those who believe the American version is superior, I ask why? British English is the most widely spoken and indeed the original, with many word stems which are deprived from the mother of all languages Latin. American English has lost many of these stems. So why is the vastly outnumbered and arguably lazy version of English the superior? I'm not trying to start an argument, I just wondered where people get this Idea from, and why other versions would tick people off so. I find some of the comments here pompous and naive.