Do you think Linux will ever threaten Microsoft's and Apple's share of the market?

Linux is only safe because it's not on the desktop. If people used Linux machines for the same purposes they use Windows machines and in the same quantities, you'd see the same security problems. Yes, Linux has threatened the server market, but there's no path I can see for Linux to threaten Microsoft's and Apple's desktop market. But I guess they won't be the kings of that market forever, and there's no more likely place than Linux for a new desktop OS to come from.