We're replacing it with native HTML video, but comparing the number of workarounds and shims needed to get feature parity across browsers and platforms, Quicktime is certainly the easier choice. It's just not future proof.
Its notorious for not being colour correct, or stable.
It also hijacked file associations without warning, which was one of the most annoying/aggressive things about it.
I'll also add that having to install bloated garbage like iTunes in the first place was aggressive (due to Apple's policy of locking iPod owners into using iTunes), so adding another piece of bloated garbage on top of that was really irritating.