Rejection Letters Are Better Than Nothing

Since I'm new at this, I'd appreciate any advice in handling markets that just don't send rejection letters.  On my blog, you're certain to hear me complain about all the form-letter rejections I keep getting.  But you know what?  I actually cherish every single rejection I get.  It's only when I get no response that I truly get frustrated.  Yes, the form-letter rejection hurts, but each one confirms the following:

• They received your manuscript.
• They looked at your manuscript.
• They don't want your manuscript.
• You're free to submit your manuscript elsewhere (where simultaneous submissions are an issue).

When you don't receive notice, then any one of these simple facts is up in the air.  Did they receive the manuscript?  Did they lose it?  Are they still considering your manuscript?  Are you free to submit elsewhere?

Over the past few years, I have submitted to several magazines, publications, publishers, and entered a few contests.  And the vast majority of them have contacted me to let me know the results.  It's the professional thing to do.

But there are a few markets that I have yet to hear from.  After a few months and a non-response to follow up queries, I can only assume that either my manuscript was rejected or they never received it.  In either case, I assume it's safe to continue on and submit the story elsewhere (though I still have this fear that someone will ding me with a simultaneous submission demerit and blackball me).

And I have yet to return to ANY of these markets.  If I don't hear from them, they're leaving me hanging.  I don't know where I stand with them, and there really is no desire to give them a second chance with another manuscript.  In my humble opinion, these markets are shooting themselves in the foot by NOT sending out rejection letters.

Hopefully, some more experienced and published writers will view this post.  If so, I have a couple of questions.  Have you had any success with markets that don't usually respond back (that is, they didn't respond to your first manuscript, but they published a subsequent one)?  Or do you also avoid those markets in the future?  How long do you wait and how many follow up query letters does it take before you assume a rejection?  Have you ever been tempted to publish a list of markets that don't respond?