Anyway, if you haven't already done so, you might want to go read the current News post about their exciting new "feature" involving linking your LiveJournal with Facebook and/or Twitter. You probably won't want to read all 80 (at last count) comment pages full of angry users but feel free to knock yourself out. (I left a comment on page 25 that's gotten 4 comments back, so clearly some people are reading through the whole thing.)
So, here's a summary of how I feel about the whole thing in terms of my journal. I don't personally have a Facebook or a Twitter account. Every now and then I'm tempted to get one or the other, but they just don't fit well with how I prefer to use the internet. At some point, I may get one or the other and feel the need to cross-post some of my content on more than one service. (I am more likely to actually start crossposting with Dreamwidth since it fits much better with how I use the internet - I am also Algeh over there but have yet to really set up the account much.) I cannot imagine that I would want to automatically cross-post everything from LiveJournal to Facebook or Twitter because it's a different kind of writing for a different kind of audience. However, if someone else wants to habitually post their LiveJournal entries to one or the other service because they use them to communicate the same information to different audiences, I see that as their business. It's their content and their choice to post it wherever they want.
Comments are trickier. In general, I see comments in my journal as a collaborative exercise among the readers of a post. While you in some sense "own" your comments, you built them with the inspiration and assistance of the post and possibly the other comments, so they're less "yours" than a post in isolation. Obviously, there are some comments that stand alone just fine. If, in a public post, I threw out some kind of general discussion prompt like "so, how do you feel about US foreign policy?" and someone replied with their overall position, I would have no problem with them also posting that comment as an entry in their journal (with or without linking back to my entry). I also wouldn't care if they posted it on Facebook or, for that matter, sent it in to the local newspaper (preferably without a link to my journal in that case). However, I'm more likely want a conversation in my comments than a bunch of disconnected op-ed pieces, and those generally would not make sense to share outside the conversation. I assume that my readers also have a basic sense of whether or not a comment of theirs stands on its own or needs to be fleshed out before being shared outside the conversation. I expect comments to my public journal entries to be treated like any other conversation in a reasonably public place where it is likely to be overheard, which means that they are not private or exclusive but also not to be mindlessly and automatically parroted somewhere else - if someone wants to listen to the conversation, they can come on over and listen here.
I expect, along with most users of the feature, that the content of my non-public posts, including comments to those posts, will not be shared outside those posts. There may be times where it makes sense for a reader to re-work a comment they wrote to a locked post and share it in a larger context, but I expect them to do it in a thoughtful, non-automated way that does not reveal its origins. (For example, if I were to write a locked post about a family matter and a reader chose to reply with a related family story of their own and then realized that their story also would make a good post for their journal, I would expect them to then re-work their comment into a post that does not reference my post's content or existence before sharing it.) My friends list has, historically been full of people who seem to share this expectation, as I have not had an issue with the content, topics, or existence of my locked posts being broadcast inappropriately. I assume that will continue and that those I have chosen to friend are the type who will not intentionally broadcast things I have chosen to keep private simply because LiveJournal has given them a very easy way to do it. If given the option (as I feel would be good practice) to disable the cross-posting of comments on locked posts I would enable it to make my feelings on the matter more clear, however.
However, I have a further concern. The new comment-sharing tickyboxes are right next to the post comment button. Worse, they are in the tab-order between typing and the post comment button for the keyboard-users, replacing the previous tab-enter behavior of posting a comment. This makes it easy for someone who is momentarily careless to accidentally check the box and end up broadcasting their comment to the entire twitterverse or facebooksphere without meaning to.
Thus, I have a request. If you choose to link your LiveJournal account to your Facebook or Twitter, I ask you to think carefully about the new responsibility you have to double-check whether you have accidentally checked those boxes before commenting in my journal. I'd strongly prefer that you not link your journal in this manner at all to prevent such accidents.
Also, feel free to go give 'em hell in the news post.