Here's another philosophy-related entry, so if you don't like such stuff, move along.

An objection that seems to come up to certain theories of mind , for example materialist ones like the one I hold, concerns qualia.

The Wikipedia link says that there are different, changing definitions of the term, but they settle on "what it's like [to feel/smell/see/be something]." Basically it sounds to me like subjective experience.

There are a couple of famous examples in philosophy. One is from the famous article by Thomas Nagel, "What is it Like to Be a Bat?" in which he asks and tries to answer that question, and ultimately concludes that there is the property of being like something that materialist explanations of mind probably will never be able to fully explain.

Another famous example is the color expert in a black and white world. Imagine a scholar who lives in a completely black and white world, but who is an expert on the color red. He knows all available information on the color red, how it hits the retina and is interpreted by the brains of those who live in a color world. So one day he opens a portal to the color world and transports back a red rose. So he's seeing the color red for the first time. Is he learning anything new?

I think the answer to the question is patently obviously true, but some philosophers apparently don't think so.

And I don't see how this is a reasonable objection against materialism. It's simply the distinction between first and second-hand information. I could store information about the color red in a computer, or I could hook the computer up to a camera and scan in color images containing red. There's a clear difference in the type of information.

What they might be getting at is awareness, consciousness, or self-awareness, but the discussion seems extremely vague and these terms are even more ill-defined than qualia, so who knows.