The SDMB is not a good place for the paranoid.
QM, the main trouble with asking someone a question in a thread is that he may never happen to come back to the thread, especially if it’s in GQ or IMHO. In those forums, we tend to post our answers and then move on. He’s not ignoring you, he just didn’t get your message.
And this actually holds true for all the forums. We can’t read all the threads all the time.
If you really want an answer to a question in a thread, you can use e-mail, or you can start a “Hey, So-and-so!” thread in MPSIMS, although that, too, has no guarantee that (a) he’ll even see it and (b) he’ll feel like answering.
And you’re perfectly entitled to put a personal message as a hijack into a thread, as long as it’s clearly labeled as a hijack. But if he doesn’t answer you, please don’t keep hammering away at it. Go to e-mail or something.