@ Cosmic Gerbil
Not a problem. And yeah, it doesn't filter out stories so if the person hasn't used their account in ages (as in, their feed on their profile page is blank) chances are they're not coming back, which is unfortunate. And not helpful if you want feedback.
Yes. So the author of the blog will state what they want to read; some people have an issue, for example, with reading stories that are NC-17 and contain themes of incest/rape. They state that in their comment swap blog. Oftentimes, they'll ask that you comment first. That's why I mentioned the "honor code"---some people will either eventually comment back and apologize if they don't get to it right away, while others, sadly, do not comment back at all. Be careful of that. There's no harm in sending them a message if you think they forgot though!
In some comment swap blogs as of late, people will ask if you kindly "recommend" their story and they might do the same for yours, which ends up in exposure for both of your pieces. I think it's a fair trade off in addition to the swapping.