Heh...didn't know there were "sonusman translators" out their.

You guys get paid for that? Is there a university degree that you have to get?
Good discussion so far.
When I first started out, I thought eq was going to create seperation, so I eq'ed til everything was SO seperated that it sounded ANNOYING.
Naturally, there will be "masking" effects when you combine instruments. The trick is to make sure that how one instrument "masks" another is not masking what is important about that instrument IN THAT MIX.
So many things come into play at that point. We start getting into the whole "it sounds great on it's own, but doesn't sound good in a mix". I have heard stuff where people thought something didn't sound good in the mix, but in reality, it offered just the right presense and/or any other descriptive.
I try to remember that every sums to the whole, and the whole is what is important. I do better work when I don't focus to closely on any one instrument in the mix.
The tracking stage is where it is all at. Man, I learn that over and over and over again. The second I have to do more than a 3 or 4 dB cut/boost on anything, I didn't get it right tracking (I am finding that most eq's, digital or analog work much better in the 3 to 4dB cut/boost range.....). Any more than that and the eq all of a sudden become "obvious".
Here is a scenario that should hit home for many, and give a few things to think about.
The snare hit's in most pop music on 2 and 4. It is a VERY short lived sound. Tell me, how terribly bad is it going to be if it "mask's" the guitar a bit? Probably isn't going to be bad at all, and certainly, letting it be a bit more prominent in the mix than the guitar for that whole 100ms it lasts (IF THAT!!!) is no crime, and you will hear on many fine sounding productions, if you listen closely that this happens all the time.
Mixing is far more art than science! I cannot usually give a lot of technical mumbo jumbo about why I eq something a certain way. I did it because it offered what sounded right for that song. I get into trouble when I start eqing something because that is what I "always do" to that kind of track.
One song may need a tight and bright snare that is not very ambiant. Another may need a loose and beefy snare that has a crap load of reverb on it. I would employ FAR different eq approaches to bring either of those out, and certainly, I would have used very different snare while tracking (if the freakin' drummer even HAD a different snare available while tracking...don't get me started on that....).
Does the bass do a lot of notes? Certainly a more articulate, midrangy sound will work better than some beefed up overly compressed low end thing. Sometimes though, the bass is just "riding the E" and needs HUGE bottom. Again, two different approaches to the eq.
Percussive vocals of lush and big? Two different approaches.
Using "pass filters" and "shelve" eq's CAN help in keeping "junk" out of the sound that doesn't need to be there, but it is only part of the equasion.
Approach your tracking with a good idea of what things need to sound like. If you are newer to this recording stuff, you will get fooled a lot by what kind of source sounds you need to make a certain type of song work. Live and learn! Learn and try something different next time.
In time, you will find yourself using less eq because you will either realize that it usually mucks up the sound if used too drastically, or because you just got it RIGHT while tracking.
Ed