For an Opera user, it's still damn annoying to have to start up another browser. I tend to have Chrome running as a fallback but it does always grate me when people don't bother to fix their sites. And it's not as if Opera was that fussy.

That depends. Out of all browsers, about 1% or less. Among the tech saavy (presumably your target customers), much more than that.

Not as a principle, but in practice: when I go to a website and it's broken, I don't exactly have great faith in the quality of their products if it's a technical offering.