Please adjust your spam-blocker so that it accepts verification once per post. When I'm posting a comment, I essentially always preview first. Sometimes I preview multiple times. It's nice that the question is irrelevant on preview, but it would be nicer still if, upon answering it correctly in a preview, one was not asked again when deciding to actually post.
That might be nice, but the application is not stateful, so it's hard to implement. (My extension is stateful, so it knows what question you're answering, but it's not capable of correlating multiple sessions.) Sorry.
Well, in terms of verification, that's already true. If you mean that the captcha shouldn't even be present if you're only previewing, well, how can I tell if you're only previewing?