Although I have never experienced this problem before, as of yesterday the comments that I leave on wordpress.com blogs where I have previously been approved did not appear immediately after I posted them. I became suspicious and did some investigation and found that the comments are ending up in the Akismet spam filter. Thus far raincoaster, sulz, thesacredpath and several other bloggers have found my comments in the Akismet filter and fished them out.
I'm aware that this is a long standing problem as witnessed by the search box results http://en.forums.wordpress.com/search.php?q=Akismet+eating+comments
At present I'm being compelled to send an email to every wordpress.com blogger who has a blog post I have commented on after I leave my comment. I'm wondering if staff can recommend any other way of dealing with this problem.