Flash video has become the de-facto standard on the web for displaying streaming video. There are many reasons for this, portability being the main one. Flash is available for Windows, Linux, Mac's, and a host of other devices.
Why then do Web 2.0 companies with Mac fans running their IT departments insist on forcing everyone to watch their tutorials, walkthroughs, screencasts, and such on Quicktime?
Quicktime isn't portable. It doesn't work well on Linux, because Apple thinks that Mac OS is the only UNIX OS out there, and don't see a need to distribute Quicktime for Linux. It's ironic, because if you include servers, there are many more Linux machines than Mac's, but that apparently doesn't matter.
I'm sure it sucked back when Mac's had to put up with everyone using Windows Media and Real Player (ugh), but that doesn't mean its right to take out those streaming video frustrations on Windows and Linux people. Quicktime sucks for Windows, frankly, and what support there is for Linux for it is spotty, at best.
Go with Flash video. You'll reach a wider audience with the least technical frustrations possible.