Monty Montgomery is perhaps best known as the main person behind the OGG audio and video formats. He is pretty knowledgable about these things, so when he says most people are asking for the wrong things, I think it is worth paying attention. He did a detailed write-up at http://people.xiph.org/~xiphmont/demo/neil-young.html. The title of the post is 24/192 Music Downlaods…and why they make no sense.
Monty gives a lot of detail on what this all means, but let’s start with what we mean by 24/192. The 24 refers to 24-bit encoding, and the 192 is a reference to 192kHz frequency range. So why are these both bad choices?
The 192kHz rqange goes beyond what human ears are capable of hearing. Despite what some people may believe, there are physiological limits to what any ear is capable of. You might think that worst-case, the extra frequencies are just wasted, but that is not all. Because your sound reproduction equipment does not have the same limitations as human ears do, the equipment will do its best to reproduce those sounds, and in so doing is likely to cause interactions that actually reduce the fidelity of the sounds you are capable of hearing. So instead of higher numbers making things better, they make things worse.
For the 24-bit, things are a little better. For the home user, going to 24-bit only wastes space by making files bigger, but does not reduce fidelity. There are special cases where using 24-bit recording in a studio while making the original recording could make sense, but the home user will probably never encounter those cases.
Monty’s bottom line is that 16-bit, 44.1kHz recording is as good as it gets, and this has been born out in controlled double-blind studies. You can read his article for the details (and you should if you are at all interested), but for the home user the result is clear: encode at 44.1kHz, 16-bit, and you will have the best recording you can hear.