It's not a desktop app or browser addon but a Pinboard archive account might work for you - <a href="http://pinboard.in/upgrade/" rel="nofollow">http://pinboard.in/upgrade/</a><p>I can't check right now but I -think- you can download the archive at any time, not just if you're closing your account (but I could be wrong.)
You can just copy off Chrome's bookmarks file. It's at ~/Library/Application Support/Google/Chrome/Default/Bookmarks